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/events/handlers/order_handlers.py

@@ -0,0 +1,22 @@
+from __future__ import annotations
+
+import logging
+
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from shared.events import register_activity_handler
+from shared.models.federation import APActivity
+
+log = logging.getLogger(__name__)
+
+
+async def on_order_created(activity: APActivity, session: AsyncSession) -> None:
+    log.info("order.created: order_id=%s", activity.object_data.get("order_id"))
+
+
+async def on_order_paid(activity: APActivity, session: AsyncSession) -> None:
+    log.info("order.paid: order_id=%s", activity.object_data.get("order_id"))
+
+
+register_activity_handler("Create", on_order_created, object_type="rose:Order")
+register_activity_handler("rose:OrderPaid", on_order_paid)