* feat(issues): persist comment collapse state across page reloads
Store collapsed comment IDs in a workspace-scoped Zustand store backed
by localStorage, replacing the transient useState(true) default.
Comments now remember their collapsed/expanded state per issue.
* test(issues): add useCommentCollapseStore mock to issue-detail tests
The existing vi.mock for @multica/core/issues/stores didn't include the
newly exported useCommentCollapseStore, causing CommentCard to throw at
render time.