test: Add comprehensive test coverage for untested modules
Add tests for previously untested components and services:
- apiKeyService.ts: localStorage operations (14 tests)
- ApiKeyModal.tsx: form validation, submission (22 tests)
- App.tsx: state transitions, error handling (23 tests)
- latexService.ts: API calls, template detection (35 tests)
- latex_service.py: LaTeX escaping, compilation (59 tests)
- server.py: Flask routes, field mapping (38 tests)
Also fix geminiService tests by adding proper apiKeyService mock.
Total new test coverage: 173 TypeScript tests, 97 Python tests
https://claude.ai/code/session_01D4k6b4nUjwfcHMvectsri2
04fe925891