Improve history compaction correctness and shared collector readability.
- Extract history retention and compaction into a dedicated module; preserve warnings when health fields are missing and select the newest equal-severity sample by timestamp.
- Reuse the shared concurrency helper for Docker collectors and handle invalid concurrency settings consistently.
- Remove duplicate translation keys while preserving the effective translations.
- Isolate Windows diagnostic smoke fixtures from installed agents and real credentials.
- Update qs to 6.17.1.
Validation: correctness lint, inline JavaScript syntax, history/concurrency regression checks, existing smoke suite, shell and PowerShell syntax, and production dependency audit passed. No separate TypeScript or application build step is defined.