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.

src/__tests__/jest-dom.d.ts

@@ -0,0 +1,12 @@
+/// <reference types="@testing-library/jest-dom" />
+
+import { type expect } from 'bun:test'
+import { type TestingLibraryMatchers } from '@testing-library/jest-dom/matchers'
+
+declare module 'bun:test' {
+  interface Matchers<T = any>
+    extends TestingLibraryMatchers<
+      ReturnType<typeof expect.stringContaining>,
+      T
+    > {}
+}