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)

account/templates/fragments/auth_menu.html

@@ -0,0 +1,36 @@
+{# Desktop auth menu #}
+<span id="auth-menu-desktop" class="hidden md:inline-flex">
+{% if user_email %}
+  <a
+    href="{{ account_url('/') }}"
+    class="justify-center cursor-pointer flex flex-row items-center p-3 gap-2 rounded bg-stone-200 text-black"
+    data-close-details
+  >
+    <i class="fa-solid fa-user"></i>
+    <span>{{ user_email }}</span>
+  </a>
+{% else %}
+  <a
+    href="{{ account_url('/') }}"
+    class="justify-center cursor-pointer flex flex-row items-center p-3 gap-2 rounded bg-stone-200 text-black"
+    data-close-details
+  >
+    <i class="fa-solid fa-key"></i>
+    <span>sign in or register</span>
+  </a>
+{% endif %}
+</span>
+{# Mobile auth menu #}
+<span id="auth-menu-mobile" class="block md:hidden text-md font-bold">
+{% if user_email %}
+  <a href="{{ account_url('/') }}" data-close-details>
+    <i class="fa-solid fa-user"></i>
+    <span>{{ user_email }}</span>
+  </a>
+{% else %}
+  <a href="{{ account_url('/') }}">
+    <i class="fa-solid fa-key"></i>
+    <span>sign in or register</span>
+  </a>
+{% endif %}
+</span>