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/static/img/filter.svg

@@ -0,0 +1,2 @@
+<?xml version="1.0" ?><!-- Uploaded to: SVG Repo, www.svgrepo.com, Generator: SVG Repo Mixer Tools -->
+<svg width="800px" height="800px" viewBox="0 0 24 24" fill="none" xmlns="http://www.w3.org/2000/svg"><path d="M18 7H17M17 7H16M17 7V6M17 7V8M12.5 5H6C5.5286 5 5.29289 5 5.14645 5.14645C5 5.29289 5 5.5286 5 6V7.96482C5 8.2268 5 8.35779 5.05916 8.46834C5.11833 8.57888 5.22732 8.65154 5.4453 8.79687L8.4688 10.8125C9.34073 11.3938 9.7767 11.6845 10.0133 12.1267C10.25 12.5688 10.25 13.0928 10.25 14.1407V19L13.75 17.25V14.1407C13.75 13.0928 13.75 12.5688 13.9867 12.1267C14.1205 11.8765 14.3182 11.6748 14.6226 11.4415M20 7C20 8.65685 18.6569 10 17 10C15.3431 10 14 8.65685 14 7C14 5.34315 15.3431 4 17 4C18.6569 4 20 5.34315 20 7Z" stroke="#464455" stroke-linecap="round" stroke-linejoin="round"/></svg>

shared/static/img/search.svg

@@ -0,0 +1,4 @@
+<?xml version="1.0" encoding="utf-8"?><!-- Uploaded to: SVG Repo, www.svgrepo.com, Generator: SVG Repo Mixer Tools -->
+<svg width="800px" height="800px" viewBox="0 0 24 24" fill="none" xmlns="http://www.w3.org/2000/svg">
+<path d="M15.7955 15.8111L21 21M18 10.5C18 14.6421 14.6421 18 10.5 18C6.35786 18 3 14.6421 3 10.5C3 6.35786 6.35786 3 10.5 3C14.6421 3 18 6.35786 18 10.5Z" stroke="#000000" stroke-width="2" stroke-linecap="round" stroke-linejoin="round"/>
+</svg>