feat(tasks): assignee inline control + "assign to me" palette verb + bulk-edit assignee

Ship the manual assignment path today.

## Scope
- Add an assignee dropdown to `apps/web/src/app/(app)/[team]/tasks/[id]/inline-controls.tsx` alongside status/priority/cycle/etc.
- Populate options from `GET /api/studio/{team}/team-members` (create if missing — returns User rows from TeamMembership).
- Add "Assign to me" as a palette verb (`command-palette.tsx`).
- Add bulk-edit toolbar option (`bulk-edit-toolbar.tsx`).

## Notes
- `PATCH /api/studio/{team}/tasks/{id}` already accepts `assigneeId`.
- Bulk endpoint already accepts it.
- No new schema needed.

## Verification
- Assign OPER-2 to Justin from the UI.
- Assign POR-395 to Sweet from the UI.
- Both assignments visible on refresh.