refactor: reduce config.py to bootstrap-only, clean up legacy full config

- Remove 450+ lines of old full config generation code
- config.yaml now manages ONLY 3 bootstrap keys (eos_connect_web_port, time_zone, log_level)
- All other settings (111 fields) are managed via web UI + SQLite store
- Improves maintainability and aligns with web-based config architecture

Includes:
- config.yaml creation on fresh install
- Fix pv_forecast list format in defaults
- Update tests to match bootstrap-only architecture
- All 914 tests pass

Author: ohAnd