feat: migrate from SQLite to PostgreSQL - complete schema and API updates

- Remove better-sqlite3, add pg driver
- Convert schema to PostgreSQL types (serial, timestamp, boolean, jsonb)
- Generate fresh PostgreSQL migrations
- Update database connection layer with pg.Pool
- Fix all API routes: remove JSON.parse/stringify, use native timestamps and booleans
- Update drizzle.config.ts and .env.example for PostgreSQL

package.json

@@ -19,13 +19,12 @@
     "@radix-ui/react-label": "^2.1.8",
     "@radix-ui/react-select": "^2.2.6",
     "@radix-ui/react-slider": "^1.3.6",
-    "@types/better-sqlite3": "^7.6.13",
     "@types/node": "^25.2.3",
     "@types/papaparse": "^5.5.2",
+    "@types/pg": "^8.11.10",
     "@types/react": "^19.2.14",
     "@types/react-dom": "^19.2.3",
     "autoprefixer": "^10.4.24",
-    "better-sqlite3": "^12.6.2",
     "class-variance-authority": "^0.7.1",
     "clsx": "^2.1.1",
     "drizzle-orm": "^0.45.1",
@@ -36,6 +35,7 @@
     "next": "^16.1.6",
     "next-themes": "^0.4.6",
     "papaparse": "^5.5.3",
+    "pg": "^8.13.1",
     "postcss": "^8.5.6",
     "react": "^19.2.4",
     "react-dom": "^19.2.4",