refactor: migrate main.py to modular routers and add project roadmap

- Migrated monolithic main.py to feature-scoped routers in app/routers/
- Added GEMINI.md for project context and AI instructional guidelines
- Updated README.md with a comprehensive modernization plan (SQL migration, robust scraping DSL, frontend modernization)
- Improved authentication with cookie support and modular JS
- Updated test suite and documentation

tests/AGENTS.md

@@ -0,0 +1,64 @@
+# AGENTS.md - Test Suite
+
+## OVERVIEW
+
+Pytest test suite for Ohm Stream Downloader with 18 test files covering unit and integration tests.
+
+## STRUCTURE
+
+```
+tests/
+├── conftest.py              # Fixtures & pytest config
+├── test_*.py                # 18 test modules
+├── test_api.py              # FastAPI endpoints (integration)
+├── test_auth.py             # JWT authentication
+├── test_download_manager.py # Download queue management
+├── test_downloaders.py     # Provider downloaders
+├── test_anime_sama_*.py    # Anime-Sama provider variants
+├── test_favorites.py        # Favorites management
+├── test_french_manga.py     # French-Manga provider
+├── test_models.py           # Pydantic model validation
+├── test_sonarr.py           # Sonarr webhook integration
+├── test_utils.py            # Utility functions
+├── test_watchlist.py        # Auto-download watchlist
+├── test_metadata_enrichment.py
+├── test_translate_api.py
+├── test_delete_and_restore.py
+```
+
+## WHERE TO LOOK
+
+| Need | File |
+|------|------|
+| Run all tests | `pytest` |
+| Unit tests only | `pytest -m "unit"` |
+| Integration tests | `pytest -m "integration"` (test_api.py auto-marked) |
+| Download logic | `test_download_manager.py`, `test_downloaders.py` |
+| API endpoints | `test_api.py` |
+| Provider scrapers | `test_anime_sama_*.py`, `test_french_manga.py` |
+
+## CONVENTIONS
+
+**Markers** (auto-applied unless manual):
+- `unit` - Default for non-api tests
+- `integration` - test_api.py only
+- `asyncio` - Auto-detected from coroutine functions
+- `slow` - Manual: `@pytest.mark.slow`
+- `network` - Manual: `@pytest.mark.network`
+
+**Naming**:
+- Files: `test_*.py`
+- Classes: `Test*` (e.g., `class TestSanitizeFilename:`)
+- Functions: `test_*` (e.g., `def test_sanitize_simple_filename(self):`)
+
+**Fixtures** (in conftest.py):
+- `temp_dir` - Temporary directory (auto-cleanup)
+- `temp_download_dir` - Download folder
+- `sample_download_task` - DownloadTask instance
+- `mock_httpx_client` - Mocked AsyncClient
+- `download_manager` - Pre-configured DownloadManager
+
+**Run commands**:
+- `pytest` - All tests with coverage
+- `pytest -m "not slow"` - Skip slow tests
+- `pytest --cov=app --cov-report=html` - HTML coverage report