fix: improve TypeScript types for better IDE code hinting

- Install @types/bun and @types/jsdom for proper type definitions
- Fix mock function typing in test files
- Create jest-dom.d.ts to properly extend Bun's Matchers interface
- Remove MockedFunction imports (not supported in Bun's types)
- Cast global.fetch and useSession mocks to any where needed
- Fix mock.module return types to match expected signatures

This resolves TypeScript errors that were preventing proper code
completion and type checking in IDEs.

package.json

@@ -65,6 +65,8 @@
     "@testing-library/react": "^16.3.2",
     "@testing-library/user-event": "^14.6.1",
     "@types/bcrypt": "^6.0.0",
+    "@types/bun": "^1.3.11",
+    "@types/jsdom": "^28.0.1",
     "@types/node": "^20",
     "@types/papaparse": "^5.5.2",
     "@types/pg": "^8.20.0",