Fix #1000: Error: Script terminated by timeout

[victorwon2001]

Fixes #1000

Implementation summary

Updated Mopidy Tracks loading to use cursor-based lookup batches and bounded ITEMS_LOADED commits, preserving order, progress, missing-result handling, and cancellation. Added focused regression coverage.

Changes

__tests__/services/mopidy/library-tracks.test.js | 216 +++++++++++++++++++++++
 src/js/services/mopidy/middleware.js             |  61 +++++--
 2 files changed, 265 insertions(+), 12 deletions(-)

Testing

Yes. Focused regression tests and repository checks passed.