Add .gitignore for Python, Node, IDE and OS artifacts

Excludes: .venv, node_modules, dist, .env, *.db, __pycache__, .DS_Store, .idea

.gitignore

+# ===== Python / Backend =====
+__pycache__/
+*.py[cod]
+*.pyo
+.venv/
+.env
+*.db
+*.db-shm
+*.db-wal
+
+# ===== Node / Frontend =====
+node_modules/
+dist/
+.vite/
+
+# ===== IDE =====
+.vscode/
+.idea/
+*.swp
+
+# ===== OS =====
+.DS_Store
+Thumbs.db
+
+# ===== Logs =====
+*.log