Fix: Retry Summarization skips re-transcription

[kimjune01]

Summary

• Retry Summarization now reuses the existing transcription from the database instead of re-running Whisper
• Adds retrySummarization(recordingID:) to ProcessingCoordinator that goes straight to the summarization phase
• Updates SummaryViewModel.retryProcessing() to route summarizationFailed and completed states through the new path

Problem

When clicking "Retry Summarization", the app ran the full pipeline: transcription → summarization. For long recordings this meant waiting several minutes for Whisper to re-transcribe audio that was already transcribed and stored in the database.

Changes

• ProcessingCoordinatorType.swift — added retrySummarization(recordingID:) to protocol
• ProcessingCoordinator.swift — implemented retrySummarization and resumeSummarization which skip transcription and use stored transcript text
• SummaryViewModel.swift — routes retry for summarizationFailed/completed states through retrySummarization instead of startProcessing

Test plan

• Trigger a recording and let it complete transcription + summarization
• Click "Retry Summarization" and verify it skips transcription (no Whisper loading/processing)
• Verify summarization completes and updates the UI
• Test retry after a summarization failure
• Verify retrying a failed transcription still re-runs the full pipeline

Fixes #12