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)

shared/browser/templates/_oob_elements.html

@@ -0,0 +1,33 @@
+{% extends oob.oob_extends %}
+
+{# OOB elements for HTMX navigation - all elements that need updating #}
+
+{# Import shared OOB macros #}
+{% from '_types/root/_oob_menu.html' import mobile_menu with context %}
+
+{% block oobs %}
+
+  {% from '_types/root/_n/macros.html' import oob_header with context %}
+  {{oob_header(
+    oob.parent_id,
+    oob.child_id,
+    oob.header,
+  )}}
+
+  {% from oob.parent_header import header_row with context %}
+  {{ header_row(oob=True) }}
+{% endblock %}
+
+
+{# Mobile menu - from market/index.html _main_mobile_menu block #}
+{% set mobile_nav %}
+  {% include oob.nav %}
+{% endset %}
+{{ mobile_menu(mobile_nav) }}
+
+
+{% block content %}
+    {% include oob.main %}
+{% endblock %}
+
+