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)

market/bp/fragments/__init__.py

@@ -0,0 +1 @@
+from .routes import register as register_fragments

market/bp/fragments/routes.py

@@ -0,0 +1,54 @@
+"""Market app fragment endpoints.
+
+Exposes HTML fragments at ``/internal/fragments/<type>`` for consumption
+by other coop apps via the fragment client.
+"""
+
+from __future__ import annotations
+
+from quart import Blueprint, Response, g, render_template, request
+
+from shared.infrastructure.fragments import FRAGMENT_HEADER
+from shared.services.registry import services
+
+
+def register():
+    bp = Blueprint("fragments", __name__, url_prefix="/internal/fragments")
+
+    _handlers: dict[str, object] = {}
+
+    @bp.before_request
+    async def _require_fragment_header():
+        if not request.headers.get(FRAGMENT_HEADER):
+            return Response("", status=403)
+
+    @bp.get("/<fragment_type>")
+    async def get_fragment(fragment_type: str):
+        handler = _handlers.get(fragment_type)
+        if handler is None:
+            return Response("", status=200, content_type="text/html")
+        html = await handler()
+        return Response(html, status=200, content_type="text/html")
+
+    # --- container-nav fragment: market links --------------------------------
+
+    async def _container_nav_handler():
+        container_type = request.args.get("container_type", "page")
+        container_id = int(request.args.get("container_id", 0))
+        post_slug = request.args.get("post_slug", "")
+
+        markets = await services.market.marketplaces_for_container(
+            g.s, container_type, container_id,
+        )
+        if not markets:
+            return ""
+        return await render_template(
+            "fragments/container_nav_markets.html",
+            markets=markets, post_slug=post_slug,
+        )
+
+    _handlers["container-nav"] = _container_nav_handler
+
+    bp._fragment_handlers = _handlers
+
+    return bp