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)

events/templates/fragments/account_nav_items.html

@@ -0,0 +1,23 @@
+{# Account nav items: tickets + bookings links for the account dashboard #}
+<div class="relative nav-group">
+  <a href="{{ account_url('/tickets/') }}"
+     hx-get="{{ account_url('/tickets/') }}"
+     hx-target="#main-panel"
+     hx-select="{{ hx_select_search }}"
+     hx-swap="outerHTML"
+     hx-push-url="true"
+     class="{{styles.nav_button}}">
+    tickets
+  </a>
+</div>
+<div class="relative nav-group">
+  <a href="{{ account_url('/bookings/') }}"
+     hx-get="{{ account_url('/bookings/') }}"
+     hx-target="#main-panel"
+     hx-select="{{ hx_select_search }}"
+     hx-swap="outerHTML"
+     hx-push-url="true"
+     class="{{styles.nav_button}}">
+    bookings
+  </a>
+</div>