- Remove instanceConfig parameter from all retriever methods (getTags, getQueue, getHistory)
- Retriever instances now use this.url, this.apiKey, this.id instead of passed parameter
- Convert ArrRetrieverRegistry from class with convenience functions to pure singleton object
- Export singleton instance directly instead of class + convenience functions
- Update poller.js and historyFetcher.js to call methods on singleton directly
- All 261 tests pass with zero behavior changes
- Create ArrRetriever abstract base class defining pluggable interface
- Implement PollingSonarrRetriever and PollingRadarrRetriever with HTTP polling
- Add ArrRetrieverRegistry for managing retriever instances
- Refactor poller.js to use retriever registry instead of direct Axios calls
- Update historyFetcher.js to use retriever registry
- Preserve all cache keys, TTLs, timing logs, SSE broadcasts, error handling
- Enable future webhook listeners without touching poller logic
