Monorepo: consolidate 7 repos into one

Combines shared, blog, market, cart, events, federation, and account
into a single repository. Eliminates submodule sync, sibling model
copying at build time, and per-app CI orchestration.

Changes:
- Remove per-app .git, .gitmodules, .gitea, submodule shared/ dirs
- Remove stale sibling model copies from each app
- Update all 6 Dockerfiles for monorepo build context (root = .)
- Add build directives to docker-compose.yml
- Add single .gitea/workflows/ci.yml with change detection
- Add .dockerignore for monorepo build context
- Create __init__.py for federation and account (cross-app imports)

federation/templates/federation/_post_card.html

@@ -0,0 +1,52 @@
+<article class="bg-white rounded-lg shadow-sm border border-stone-200 p-4 mb-4">
+  {% if item.boosted_by %}
+    <div class="text-sm text-stone-500 mb-2">
+      Boosted by {{ item.boosted_by }}
+    </div>
+  {% endif %}
+
+  <div class="flex items-start gap-3">
+    {% if item.actor_icon %}
+      <img src="{{ item.actor_icon }}" alt="" class="w-10 h-10 rounded-full">
+    {% else %}
+      <div class="w-10 h-10 rounded-full bg-stone-300 flex items-center justify-center text-stone-600 font-bold text-sm">
+        {{ item.actor_name[0] | upper if item.actor_name else '?' }}
+      </div>
+    {% endif %}
+
+    <div class="flex-1 min-w-0">
+      <div class="flex items-baseline gap-2">
+        <span class="font-semibold text-stone-900">{{ item.actor_name }}</span>
+        <span class="text-sm text-stone-500">
+          @{{ item.actor_username }}{% if item.actor_domain %}@{{ item.actor_domain }}{% endif %}
+        </span>
+        <span class="text-sm text-stone-400 ml-auto">
+          {% if item.published %}
+            {{ item.published.strftime('%b %d, %H:%M') }}
+          {% endif %}
+        </span>
+      </div>
+
+      {% if item.summary %}
+        <details class="mt-2">
+          <summary class="text-stone-500 cursor-pointer">CW: {{ item.summary }}</summary>
+          <div class="mt-2 prose prose-sm prose-stone max-w-none">{{ item.content | safe }}</div>
+        </details>
+      {% else %}
+        <div class="mt-2 prose prose-sm prose-stone max-w-none">{{ item.content | safe }}</div>
+      {% endif %}
+
+      {% if item.url and item.post_type == "remote" %}
+        <a href="{{ item.url }}" target="_blank" rel="noopener" class="text-sm text-stone-400 hover:underline mt-1 inline-block">
+          original
+        </a>
+      {% endif %}
+
+      {% if actor %}
+        <div id="interactions-{{ item.object_id | replace('/', '_') | replace(':', '_') }}">
+          {% include "federation/_interaction_buttons.html" with context %}
+        </div>
+      {% endif %}
+    </div>
+  </div>
+</article>