Add Assignee and Creator filter categories to the issue board filter menu,
using DropdownMenu sub-menus with hover-visible checkboxes (shadcn official
data-selected pattern from PR #6862).
Key changes:
- view-store: add assigneeFilters, includeNoAssignee, creatorFilters state
with positive selection model (empty = no filter, selected = show only matching)
- issues-header: two-level DropdownMenu — category list → sub-menu with
searchable checkbox items, issue counts, avatar grouping (Members/Agents)
- utils/filter: extract shared filterIssues() to eliminate duplication
between issues-page and issues-header
- Workspace switch clears actor filters via deferred subscription
(dynamic import to avoid circular dependency)
- 10 new filter behavior tests covering assignee, creator, no-assignee,
and combined filter scenarios
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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