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/browse/services/slugs.py

@@ -0,0 +1,24 @@
+import re
+from urllib.parse import urljoin, urlparse
+from shared.config import config
+
+def product_slug_from_href(href: str) -> str:
+    p = urlparse(href)
+    parts = [x for x in p.path.split("/") if x]
+    if not parts:
+        return ""
+    last = parts[-1]
+    if last.endswith(".html"):
+        last = last[:-5]
+    elif last.endswith(".htm"):
+        last = last[:-4]
+    last = re.sub(r"-(html|htm)+$", "", last, flags=re.I)
+    return f"{last}-html"
+
+def canonical_html_slug(slug: str) -> str:
+    base = re.sub(r"-(html|htm)+$", "", slug, flags=re.I)
+    return f"{base}-html"
+
+def suma_href_from_html_slug(slug: str) -> str:
+    canon = canonical_html_slug(slug)
+    return urljoin(config()["base_url"], f"/{canon}.html")