Recover missing album tracks during incremental scans

[lostf1sh]

Incremental sync can leave an imported album incomplete when MediaStore exposes additional tracks with timestamps older than the last sync. The folder picker can count all 16 files while the library still shows only the 3 tracks imported earlier.

Compare the eligible MediaStore IDs with the local database during the existing deletion scan. If any IDs are missing locally, query without a timestamp cutoff and retain the existing unchanged-song checks and metadata-edit preservation. Normal incremental scans resume once the IDs match.

Related to #126. The reporter's original files were unavailable; the regression test covers a reproducible cause of the reported mismatch.

Validation:

• Kotlin compilation and the full JVM test suite passed, including a rerun after updating to the latest main.
• All 3 SyncWorkerTest instrumented tests passed on Android 16. The new regression failed with 3/16 tracks before the fix and recovered all 16 afterward, preserved an edited title, and verified that the next scan uses its timestamp filter again.
• lintDebug ran and reported 94 existing errors in unchanged playback and translation files; none are in the changed code.

[greptile-apps]

Confidence Score: 5/5

The PR appears safe to merge, with no actionable correctness, security, or repository-rule violations identified.

Summary

This PR makes incremental local-library synchronization recover eligible MediaStore tracks whose timestamps predate the current sync watermark.

• Compares eligible MediaStore IDs with locally stored MediaStore IDs during reconciliation.
• Removes the timestamp cutoff when eligible tracks are missing locally while retaining unchanged-song filtering and user-edit preservation.
• Adds an instrumented regression test covering incomplete-album recovery, edited-title preservation, and restoration of normal incremental filtering.

Diagram

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[Incremental sync starts] --> B[Read local MediaStore IDs]
    B --> C[Read current eligible MediaStore IDs]
    C --> D{Eligible ID missing locally?}
    D -- No --> E[Query with incremental timestamp cutoff]
    D -- Yes --> F[Query without timestamp cutoff]
    E --> G[Apply unchanged-song checks]
    F --> G
    G --> H[Preserve user-edited metadata]
    H --> I[Upsert changed and missing tracks]
    I --> J[Next scan compares IDs again]

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