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/navigation.py

@@ -0,0 +1,32 @@
+from __future__ import annotations
+
+from sqlalchemy import select
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from shared.models.menu_node import MenuNode
+
+
+async def get_navigation_tree(session: AsyncSession) -> list[MenuNode]:
+    """
+    Return top-level menu nodes ordered by sort_order.
+
+    All apps call this directly (shared DB) — no more HTTP API.
+    """
+    result = await session.execute(
+        select(MenuNode)
+        .where(MenuNode.deleted_at.is_(None), MenuNode.depth == 0)
+        .order_by(MenuNode.sort_order.asc(), MenuNode.id.asc())
+    )
+    return list(result.scalars().all())
+
+
+async def rebuild_navigation(session: AsyncSession) -> None:
+    """
+    Rebuild menu_nodes from container_relations.
+
+    Called by event handlers when relationships change.
+    Currently a no-op placeholder — menu nodes are managed directly
+    by the admin UI. When the full relationship-driven nav is needed,
+    this will sync ContainerRelation -> MenuNode.
+    """
+    pass