When Sonarr and Radarr had the same instance ID (e.g., 'i3omb'),
the Radarr retriever would overwrite the Sonarr retriever in the Map.
This caused webhook refreshes to show '0 instance(s)' for Sonarr.
Now uses ':' as the unique key so both can coexist.
- 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
