feat(sender): add outgoing Webmention pipeline

Scan generated h-entry documents for Webmention targets and track source
revisions and delivery state in the database.

Discover target endpoints, send Webmentions asynchronously, and reconcile
updated, removed, restored, and deleted sources across scans.

Add authenticated views for inspecting sent Webmentions and make the scanner
schedule configurable.

4 files changed, 220 insertions, 3 deletions

diff --git a/webmentions_ssg/templates/base.html b/webmentions_ssg/templates/base.html
index 237a437..eb11b8e 100644
--- a/webmentions_ssg/templates/base.html
+++ b/webmentions_ssg/templates/base.html
@@ -22,8 +22,9 @@
           {% if current_user.is_authenticated %}
             <div class="navbar-nav flex-row gap-3">
               <a class="nav-link{% if request.endpoint == 'root.received' %} active{% endif %}"
-                 href="{{ url_for("root.received") }}">Received</a>
-              <span class="nav-link disabled">Sent</span>
+                 href='{{ url_for("root.received") }}'>Received</a>
+              <a class="nav-link{% if request.endpoint == 'root.sent' %} active{% endif %}"
+                 href='{{ url_for("root.sent") }}'>Sent</a>
               <a class="nav-link" href="{{ url_for("root.logout") }}">Logout</a>
             </div>
           {% endif %}
diff --git a/webmentions_ssg/templates/received.html b/webmentions_ssg/templates/received.html
index 64f225e..a44b706 100644
--- a/webmentions_ssg/templates/received.html
+++ b/webmentions_ssg/templates/received.html
@@ -3,7 +3,7 @@
 {% from "bootstrap5/pagination.html" import render_pagination %}
 {% block content %}
   <div class="d-flex justify-content-between align-items-center mb-3">
-    <h1 class="h3 mb-0">Received Webmentions</h1>
+    <h1 class="mb-0">Received Webmentions</h1>
     <span class="text-body-secondary">{{ webmentions.total }} total</span>
   </div>
   {% if webmentions.items %}
diff --git a/webmentions_ssg/templates/sent.html b/webmentions_ssg/templates/sent.html
new file mode 100644
index 0000000..69a91d8
--- /dev/null
+++ b/webmentions_ssg/templates/sent.html
@@ -0,0 +1,61 @@
+{% extends "base.html" %}
+{% from "bootstrap5/pagination.html" import render_pagination %}
+{% block content %}
+  <div class="d-flex justify-content-between align-items-center mb-3">
+    <h1 class="mb-0">Sources</h1>
+    <span class="text-body-secondary">{{ sources.total }} sources</span>
+  </div>
+  {% if sources.items %}
+    <div class="table-responsive">
+      <table class="table table-bordered table-striped table-hover align-middle">
+        <thead>
+          <tr>
+            <th scope="col">Path</th>
+            <th scope="col">URL</th>
+            <th scope="col">Webmentions</th>
+            <th scope="col">Revision</th>
+            <th scope="col">Created</th>
+            <th scope="col">Last seen</th>
+            <th scope="col">Status</th>
+          </tr>
+        </thead>
+        <tbody>
+          {% for source in sources %}
+            <tr>
+              <td class="text-nowrap">
+                <a href="{{ url_for('root.sent_source', identifier=source.uuid) }}">{{ source.path }}</a>
+              </td>
+              <td class="text-break">
+                <a href="{{ source.url }}">{{ source.url }}</a>
+              </td>
+              <td>{{ source.sent_webmentions | length }}</td>
+              <td>{{ source.revision }}</td>
+              <td class="text-nowrap">
+                <time datetime="{{ source.created_at.isoformat() }}">
+                  {{ source.created_at.strftime("%Y-%m-%d %H:%M:%S") }}
+                </time>
+              </td>
+              <td class="text-nowrap">
+                <time datetime="{{ source.last_seen_at.isoformat() }}">
+                  {{ source.last_seen_at.strftime("%Y-%m-%d %H:%M:%S") }}
+                </time>
+              </td>
+              <td>
+                {% if source.deleted_at is none %}
+                  <span class="badge text-bg-success">Active</span>
+                {% else %}
+                  <span class="badge text-bg-danger">Deleted</span>
+                {% endif %}
+              </td>
+            </tr>
+          {% endfor %}
+        </tbody>
+      </table>
+    </div>
+    {% if sources.pages > 1 %}
+      <div class="mt-3">{{ render_pagination(sources) }}</div>
+    {% endif %}
+  {% else %}
+    <p class="text-body-secondary">No Webmention sources have been discovered yet.</p>
+  {% endif %}
+{% endblock %}
diff --git a/webmentions_ssg/templates/sent_source.html b/webmentions_ssg/templates/sent_source.html
new file mode 100644
index 0000000..6d397f2
--- /dev/null
+++ b/webmentions_ssg/templates/sent_source.html
@@ -0,0 +1,155 @@
+{% extends "base.html" %}
+{% block content %}
+  <div class="mb-3">
+    <a href="{{ url_for("root.sent") }}">&larr; Back to sources</a>
+  </div>
+  <div class="d-flex justify-content-between align-items-start mb-3">
+    <h1 class="mb-0">Source Details</h1>
+  </div>
+  <div class="d-flex justify-content-between align-items-start mb-3">
+    <dl class="row">
+      <dt class="col-sm-2">UUID</dt>
+      <dd class="col-sm-4">
+        {{ source.uuid }}
+      </dd>
+      <dt class="col-sm-2">Hash</dt>
+      <dd class="col-sm-4">
+        {{ source.content_hash }}
+      </dd>
+      <dt class="col-sm-2">Path</dt>
+      <dd class="col-sm-4">
+        {{ source.path }}
+      </dd>
+      <dt class="col-sm-2">URL</dt>
+      <dd class="col-sm-4">
+        <a href="{{ source.url }}" class="text-break">{{ source.url }}</a>
+      </dd>
+      <dt class="col-sm-2">Created at</dt>
+      <dd class="col-sm-4">
+        <time datetime="{{ source.created_at.isoformat() }}">
+          {{ source.created_at.strftime("%Y-%m-%d %H:%M:%S") }}
+        </time>
+      </dd>
+      <dt class="col-sm-2">Last seen at</dt>
+      <dd class="col-sm-4">
+        <time datetime="{{ source.last_seen_at.isoformat() }}">
+          {{ source.last_seen_at.strftime("%Y-%m-%d %H:%M:%S") }}
+        </time>
+      </dd>
+      <dt class="col-sm-2">Revised at</dt>
+      <dd class="col-sm-4">
+        <time datetime="{{ source.revised_at.isoformat() }}">
+          {{ source.revised_at.strftime("%Y-%m-%d %H:%M:%S") }}
+        </time>
+      </dd>
+      <dt class="col-sm-2">Deleted at</dt>
+      <dd class="col-sm-4">
+        {% if source.deleted_at is none %}
+          N/A
+        {% else %}
+          <time datetime="{{ source.deleted_at.isoformat() }}">
+            {{ source.deleted_at.strftime("%Y-%m-%d %H:%M:%S") }}
+          </time>
+        {% endif %}
+      </dd>
+      <dt class="col-sm-2">Revision</dt>
+      <dd class="col-sm-4">
+        {{ source.revision }}
+      </dd>
+    </dl>
+  </div>
+  <div class="d-flex justify-content-between align-items-start mb-3">
+    <h2 class="mb-0">Sent Webmentions</h2>
+    <span class="text-body-secondary">{{ webmentions | length }} webmentions</span>
+  </div>
+  {% if webmentions %}
+    <div class="table-responsive">
+      <table class="table table-bordered table-striped table-hover align-middle">
+        <thead>
+          <tr>
+            <th scope="col">Target</th>
+            <th scope="col">Status</th>
+            <th scope="col">Active</th>
+            <th scope="col">Desired revision</th>
+            <th scope="col">Processed revision</th>
+            <th scope="col">Sent revision</th>
+            <th scope="col">Failure Reason</th>
+            <th scope="col">Endpoint</th>
+            <th scope="col">Response Status</th>
+            <th scope="col">Status URL</th>
+            <th scope="col">Last Attempted at</th>
+            <th scope="col">Last Sent at</th>
+          </tr>
+        </thead>
+        <tbody>
+          {% for webmention in webmentions %}
+            <tr>
+              <td class="text-break">
+                <a href="{{ webmention.target }}">{{ webmention.target }}</a>
+              </td>
+              <td>{{ webmention.status.value }}</td>
+              <td>
+                {% if webmention.active %}
+                  <span class="badge text-bg-success">Active</span>
+                {% else %}
+                  <span class="badge text-bg-secondary">Removed</span>
+                {% endif %}
+              </td>
+              <td>{{ webmention.desired_revision }}</td>
+              <td>
+                {{ webmention.processed_revision
+                if webmention.processed_revision is not none
+                else "—" }}
+              </td>
+              <td>
+                {{ webmention.sent_revision
+                if webmention.sent_revision is not none
+                else "—" }}
+              </td>
+              <td>
+                {{ webmention.failure_reason
+                if webmention.failure_reason is not none
+                else "—" }}
+              </td>
+              <td>
+                {{ webmention.endpoint
+                if webmention.endpoint is not none
+                else "—" }}
+              </td>
+              <td>
+                {{ webmention.response_status
+                if webmention.response_status is not none
+                else "—" }}
+              </td>
+              <td>
+                {{ webmention.status_url
+                if webmention.status_url is not none
+                else "—" }}
+              </td>
+              <td>
+                {% if webmention.last_attempted_at is not none %}
+                  <time datetime="{{ webmention.last_attempted_at.isoformat() }}">
+                    {{ webmention.last_attempted_at.strftime("%Y-%m-%d %H:%M:%S") }}
+                  </time>
+                {% else %}
+                  —
+                {% endif %}
+              </td>
+              <td>
+                {% if webmention.last_sent_at is not none %}
+                  <time datetime="{{ webmention.last_sent_at.isoformat() }}">
+                    {{ webmention.last_sent_at.strftime("%Y-%m-%d %H:%M:%S") }}
+                  </time>
+                {% else %}
+                  —
+                {% endif %}
+              </td>
+            </tr>
+          {% endfor %}
+        </tbody>
+      </table>
+    </div>
+  {% else %}
+    <p class="text-body-secondary">No Webmentions have been discovered for this source.</p>
+  {% endif %}
+{% endblock %}