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/scrape/build_snapshot/tools/valid_subs.py

@@ -0,0 +1,16 @@
+from typing import Dict, Set
+
+# make valid subs for ewch top in nav
+def valid_subs(nav: Dict[str, Dict])->Dict[str, Set[str]] :
+    valid_subs_by_top: Dict[str, Set[str]] = {}
+    for label, data in (nav.get("cats") or {}).items():
+        top_slug = (data or {}).get("slug")
+        if not top_slug:
+            continue
+        subs_set = {
+            (s.get("slug") or "").strip()
+            for s in (data.get("subs") or [])
+            if s.get("slug")
+        }
+        valid_subs_by_top[top_slug] = subs_set
+    return valid_subs_by_top