test: add unit tests for SenderModelService, runOrQueueSenderTraining, and updateBlock hook
- SenderModelServiceTest: 6 tests covering activation threshold (99/100),
retrain delta (149/150), runNow flag (queued vs triggered)
- OcrTrainingServiceTest: 3 tests for runOrQueueSenderTraining — idle returns
true, running saves QUEUED, duplicate QUEUED coalesces
- TranscriptionServiceTest: 3 tests for updateBlock — sets source=MANUAL,
triggers training for HANDWRITING_KURRENT with sender, skips when no sender
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>