CMRT 28: DAO: Quality-based canonical re-election on track deletion

[Swarnadip-Kar]

Finishes the TODO(XXX) left in clearFingerprintData()
"Update this logic to select next canonical track ... instead of just
promoting the first member found in the group."

Changes

When the canonical track of a group is deleted:

1. Look at every other member's quality_score; highest wins.
2. Promote it via updateCanonicalTrack() + saveFingerprintMetadata()
   (is_canonical=1, cmrt_offset_seconds=0) + updateMemberOffset()
   (offset_from_canonical=0) -- all three methods already exist from
   CMRT 27, so this PR adds zero new DAO surface.
3. Recompute every other remaining member's offset against the new
   canonical's .chroma file via FingerprintMatcher::compare().
4. Unchanged: if there are no other members, delete the now-empty group.

Notes for reviewers

• Tie-breaking on quality_score is "first highest wins" (>, not >=) --
  not expected to matter since identical scores would need byte-identical
  files, which the SHA-256 cache already catches elsewhere, but noted in
  case that assumption doesn't hold for some library.
• Same O(member count) .chroma-read cost as CmrtGroupingService::
  replaceCanonical() in CMRT 27, for the same reason (small group sizes
  expected in practice).
• All of this still runs inside clearFingerprintData()'s existing
  ScopedTransaction -- no new transaction boundaries, every new early
  return relies on the same rollback-on-destruct behavior the rest of the
  function already does.

Depends on: cmrt-pipeline-grouping (#36)

[coveralls]

Coverage Report for CI Build 27872505024

Coverage increased (+4.2%) to 34.491%

Details

• Coverage increased (+4.2%) from the base build.
• Patch coverage: 48 uncovered changes across 1 file (0 of 48 lines covered, 0.0%).
• No coverage regressions found.

Uncovered Changes

File	Changed	Covered	%
src/library/dao/trackfingerprintdao.cpp	48	0	0.0%

Coverage Regressions

No coverage regressions found.

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Coverage Stats

Relevant Lines:	89209
Covered Lines:	30769
Line Coverage:	34.49%
Coverage Strength:	77204.85 hits per line

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💛 - Coveralls