feat: add Dockerfile and .dockerignore, refactor backend to use DATA_DIR for database and uploads

Now able to use docker image

.gitignore

@@ -8,26 +8,19 @@ dist/
 frontend/dist/
 backend/dist/
 
-# SQLite database and uploads
-backend/db.sqlite
-backend/uploads/
+# Persistent backend data (database and uploads)
+backend/data/
 
 # Logs
 logs/
 *.log
 npm-debug.log*
 yarn-debug.log*
-pnpm-debug.log*
 
 # Editor directories and files
 .vscode/
 .idea/
 .DS_Store
-*.suo
-*.ntvs*
-*.njsproj
-*.sln
-*.sw?
 
 # Environment files (if any)
 .env