fix: stop bulkStar from reporting false success on partial/total failure

[Bryandero98]

Summary

• Fixes MediaCollectionDetail: bulkStar fires uncoordinated per-item error toasts and reports false overall success on failure #6018
• bulkStar in client/src/pages/MediaCollectionDetail.jsx looped over updateAnnotation calls, ignored the result entirely, and unconditionally fired a success toast — while useMediaAnnotations.js's updateAnnotation already toasted an individual error for every failure. For a batch with failures the user saw a burst of error toasts followed by a contradictory success toast, and the optimistic UI update for failed items had already been reverted despite the success message.
• updateAnnotation now accepts a { silent } option (suppresses the per-item error toast for batch callers) and returns { ok, entry } instead of a bare entry. This was necessary beyond what the issue described: entry alone can't signal success vs. failure, because the server legitimately returns entry: null on a real success too (unstarring an item with no note clears its annotation entirely, per server/routes/mediaAnnotations.js's own doc comment) — so the old res?.entry ?? null return was ambiguous between "cleared successfully" and "failed."
• bulkStar now calls with { silent: true }, counts successes/failures, and shows exactly one consolidated toast: success when all succeed, an error when all fail, and a combined "N succeeded; M failed" error on partial failure.

Test plan

• Added 3 tests in MediaCollectionDetail.test.jsx covering all-success, all-failure, and partial-failure toast behavior (made updateAnnotation a controllable mock for this).
• cd client && npx vitest run src/pages/MediaCollectionDetail.test.jsx src/hooks/useMediaAnnotations.test.jsx → 15/15 passed.
• Also ran the other 4 test files that exercise useMediaAnnotations (ImageGen.*.test.jsx) to check for regressions from the return-shape change → 17/17 passed.

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