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/product/registry.py

@@ -0,0 +1,20 @@
+
+from __future__ import annotations
+from typing import Callable, Dict, List, Union
+
+Extractor = Callable[[object, str], Dict[str, Union[str, float, int, list, dict, None]]]
+REGISTRY: List[Extractor] = []
+
+def extractor(fn: Extractor) -> Extractor:
+    """Decorator to register an extractor."""
+    REGISTRY.append(fn)
+    return fn
+
+def merge_missing(dst: dict, src: dict) -> None:
+    """
+    Merge src into dst. Only write keys that are missing or empty in dst.
+    "Empty" means None, "", [], {}.
+    """
+    for k, v in (src or {}).items():
+        if k not in dst or dst[k] in (None, "", [], {}):
+            dst[k] = v