Add per-segment review reasons for plugins

[Dicur3x]

Summary

• add a review_reasons list to transcription segments for post-processing plugins
• persist the reasons as JSON across completed, skipped, replaced, and legacy cached transcriptions
• migrate existing databases with an empty-list default, preserving existing segment text
• highlight affected rows in the transcription viewer and show every reason in a tooltip

Motivation

after_transcription plugins can currently rewrite segments, but they have no non-destructive way to ask the user to review a specific row. This adds that viewer integration without implementing or coupling Buzz to a particular detector.

This supports #1570. A repetition/hallucination detector can be proposed separately after the segment contract is agreed on.

Tests

• database migration from the previous segment schema
• review-reason persistence through all three segment save paths
• viewer background and tooltip roles
• Python compile check and Ruff check on the changed files

[raivisdejus]

@Dicur3x Thanks for your contribution!

Let's make the new data field more universal, say metadata not review_reasons and let's make it store key-value pairs, say a list of dicts. This will let us store more data for different future plugins.

I would also add such metadata field on the transcription DB entries for the same future flexibility

Tooltip could show Key: vaue list for now.