Support WebUI API Key auth, newer add responses, and cookie sync so qBittorrent 5.2 can connect reliably while keeping legacy fallback behavior.
Fixes#5724
- Eliminate support for LLM_DISABLE_THINKING and LLM_REASONING_EFFORT in config, code, and tests
- Simplify LLM thinking level logic to rely solely on LLM_THINKING_LEVEL
- Refactor LLMHelper and related endpoints to remove legacy parameter handling
- Update system API and test utilities to match new configuration structure
- Minor code cleanup and formatting improvements