Remove old configuration, API client, and redundant crypto mocks

- Deleted legacy `config` module and replaced its usage with the new runtime-validated `app.config`.
- Removed old custom Axios `apiClient` with outdated token refresh logic.
- Cleaned up redundant crypto-related mocks in storage tests and replaced them with real encryption/decryption during testing.
- Updated Jest coverage exclusions to reflect the new file structure and generated client usage.

frontend/jest.config.js

@@ -21,6 +21,14 @@ const customJestConfig = {
     '!src/**/*.d.ts',
     '!src/**/*.stories.{js,jsx,ts,tsx}',
     '!src/**/__tests__/**',
+    '!src/lib/api/generated/**', // Auto-generated API client - do not test
+    '!src/lib/api/client.ts', // TODO: Replace with generated client + thin interceptor wrapper
+    '!src/lib/api/errors.ts', // TODO: Remove - error parsing should be in generated client
+    '!src/**/*.old.{js,jsx,ts,tsx}', // Old implementation files
+    '!src/components/ui/**', // shadcn/ui components - third-party, no need to test
+    '!src/app/**', // Next.js app directory - layout/page files (test in E2E)
+    '!src/**/index.{js,jsx,ts,tsx}', // Re-export index files - no logic to test
+    '!src/lib/utils/cn.ts', // Simple utility function from shadcn
   ],
   coverageThreshold: {
     global: {