File-size decomposition (no behavior change). Move the localStorage comment-cache
methods (getCommentCacheKey, handleCommentCacheError, getCachedComments,
cacheComments, removeCommentCache, clearCommentCache, persistCommentCache,
serializeCommentsForCache) into js/services/commentThreadCache.js as functions
that take the service instance; the service keeps thin delegators so all call
sites are unchanged. Cache constants moved with them; FIVE_MINUTES_MS import
dropped from the service.
commentThreadService.js: 1296 -> 1100 lines (below its original 1122 baseline;
re-recorded to 1100).
Build + full unit suite green.
Co-Authored-By: Claude Opus 4.8 <[email protected]>
