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)

shared/browser/app/utils/__init__.py

@@ -0,0 +1,12 @@
+from .parse import (
+  parse_time,
+  parse_cost,
+  parse_dt
+)
+from .utils import (
+  current_route_relative_path,
+  current_url_without_page,
+  vary,
+)
+
+from .utc import utcnow