Add structured logging, config validation, thread-safe cache, and Selenium improvements

[natiixnt]

Summary

• Structured logging: Replace status.py print/termcolor output with Python's logging module. Logs rotate at 5MB with 3 backups in .mp/mpv2.log. Console output remains colored for backwards compatibility. Exposes get_logger() for modules that need direct logger access.
• Config validation: New validate_config() function with schema-based checking -- verifies required keys exist, types match, email sub-structure is complete, imagemagick_path exists on disk, and stt_provider is a known value. Runs automatically at startup in main.py and prints all issues as warnings so users can fix their config before hitting cryptic errors later.
• Thread-safe cache: All JSON cache reads now use fcntl.LOCK_SH (shared locks), all writes use atomic temp-file + os.replace() with fcntl.LOCK_EX (exclusive locks). This prevents cache corruption when multiple CRON jobs run concurrently against the same .mp/*.json files.
• Selenium improvements: Replace hardcoded time.sleep() waits in YouTube upload_video() with WebDriverWait + explicit expected_conditions (presence/clickability). Adds automatic screenshot capture on upload failure for debugging. Adds helper methods _wait_and_find() and _wait_and_click().
• Cleanup: Replace stray print(colored(...)) calls in YouTube.py and Outreach.py with proper info()/error()/success() functions.
• Tests: 33 new tests covering config validation, atomic cache writes, file locking, and structured logging.

Test plan

• All 33 tests pass locally (python -m pytest tests/ -v)
• Manual smoke test of python src/main.py to verify config validation prints warnings for missing/invalid values
• Verify .mp/mpv2.log is created after first run