fix(cue): preserve per-track metadata and isolate cache variants

[markojurkovic]

Summary

Fix CUE tracks losing or sharing per-track metadata when playlist entries are inserted, reloaded, or served from the metadata cache.

Changes

• Give logical CUE metadata precedence over tags from the shared underlying audio file.
• Apply preloaded CUE metadata after playlist insertion so KVO and row bindings observe the correct per-entry values.
• Use the same metadata-merging behavior for initial, asynchronous, and synchronous playlist loading.
• Keep CUE-aware and skipCue metadata/property cache entries separate.
• Replace plug-in dictionary category merges with explicit merges to avoid Objective-C selector collisions changing merge precedence.

Result

Each CUE track retains its own title and track metadata instead of inheriting shared-file tags or another track’s displayed values. Queries made with and without CUE processing also no longer contaminate one another through the cache.

Verification

• Debug arm64 build completed successfully with code signing disabled.
• git diff --check main...fix/cue-metadata-integrity passes.

Suggested manual checks

• Load a multi-track CUE sheet whose tracks have distinct titles.
• Confirm every playlist row displays the correct title immediately after insertion.
• Reload metadata and confirm the titles remain correct.
• Exercise metadata lookups both with and without CUE processing and confirm their results remain independent.