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)

cart/bp/cart/overview_routes.py

@@ -0,0 +1,31 @@
+# bp/cart/overview_routes.py — Cart overview (list of page carts)
+
+from __future__ import annotations
+
+from quart import Blueprint, render_template, make_response
+
+from shared.browser.app.utils.htmx import is_htmx_request
+from .services import get_cart_grouped_by_page
+
+
+def register(url_prefix: str) -> Blueprint:
+    bp = Blueprint("cart_overview", __name__, url_prefix=url_prefix)
+
+    @bp.get("/")
+    async def overview():
+        from quart import g
+        page_groups = await get_cart_grouped_by_page(g.s)
+
+        if not is_htmx_request():
+            html = await render_template(
+                "_types/cart/overview/index.html",
+                page_groups=page_groups,
+            )
+        else:
+            html = await render_template(
+                "_types/cart/overview/_oob_elements.html",
+                page_groups=page_groups,
+            )
+        return await make_response(html)
+
+    return bp