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/services/widgets/__init__.py

@@ -0,0 +1,22 @@
+"""Per-domain widget registration.
+
+Called once at startup after domain services are registered.
+Only registers widgets for domains that are actually available.
+"""
+from __future__ import annotations
+
+
+def register_all_widgets() -> None:
+    from shared.services.registry import services
+
+    if services.has("calendar"):
+        from .calendar_widgets import register_calendar_widgets
+        register_calendar_widgets()
+
+    if services.has("market"):
+        from .market_widgets import register_market_widgets
+        register_market_widgets()
+
+    if services.has("cart"):
+        from .cart_widgets import register_cart_widgets
+        register_cart_widgets()

shared/services/widgets/calendar_widgets.py

@@ -0,0 +1,10 @@
+"""Calendar-domain widgets.
+
+All calendar widgets have been replaced by fragments
+(events app serves them at /internal/fragments/).
+"""
+from __future__ import annotations
+
+
+def register_calendar_widgets() -> None:
+    pass

shared/services/widgets/cart_widgets.py

@@ -0,0 +1,10 @@
+"""Cart-domain widgets.
+
+Account nav link has been replaced by fragments
+(cart app serves account-nav-item at /internal/fragments/).
+"""
+from __future__ import annotations
+
+
+def register_cart_widgets() -> None:
+    pass

shared/services/widgets/market_widgets.py

@@ -0,0 +1,10 @@
+"""Market-domain widgets.
+
+Container nav widgets have been replaced by fragments
+(market app serves them at /internal/fragments/).
+"""
+from __future__ import annotations
+
+
+def register_market_widgets() -> None:
+    pass