📝 docs: add Astro Starlight public documentation site

Add comprehensive documentation site using Astro Starlight with:
- Getting Started guides (introduction, quick-start, project structure)
- Development docs (local dev, env vars, docker, migrations, testing)
- Architecture docs (overview, auth, backend, web, mobile, storage, search)
- Guidelines (code style, error handling, database, design/UX)
- Deployment docs (overview, Cloudflare Pages, Mac Mini, self-hosting)
- Project pages (overview, chat)
- API reference structure

Features:
- Dark mode support
- Full-text search (Pagefind)
- Tailwind CSS styling
- Cloudflare Pages deployment ready
- Edit on GitHub links

apps/docs/tsconfig.json

@@ -0,0 +1,9 @@
+{
+	"extends": "astro/tsconfigs/strict",
+	"compilerOptions": {
+		"baseUrl": ".",
+		"paths": {
+			"@/*": ["src/*"]
+		}
+	}
+}