Remove unused backend infrastructure and template files for Gallus CMS.

- Deleted `backend/.env.local`, admin page, and OAuth callback page.
- Removed legacy Docker configurations [`docker-compose.yml`, `Dockerfile.caddy`].
- Deprecated migration script, unused routes, and event/gallery migration documentation.
- Updated gitignore to reflect removed folder structure.

backend/package.json

@@ -9,15 +9,14 @@
     "start": "node dist/index.js",
     "db:generate": "drizzle-kit generate",
     "db:migrate": "drizzle-kit migrate",
-    "db:studio": "drizzle-kit studio",
-    "migrate:old-data": "tsx src/scripts/migrate-old-data.ts"
+    "db:studio": "drizzle-kit studio"
   },
   "dependencies": {
     "@fastify/cookie": "^9.3.1",
     "@fastify/cors": "^9.0.1",
     "@fastify/jwt": "^8.0.0",
-    "@fastify/static": "^6.12.0",
     "@fastify/multipart": "^8.1.0",
+    "@fastify/session": "^10.8.0",
     "bcrypt": "^5.1.1",
     "better-sqlite3": "^11.10.0",
     "drizzle-orm": "^0.33.0",