feat: add combobox component

docs/CHECKLIST.md

@@ -9,7 +9,8 @@ is the first downstream consumer; its screens drive the order.
 
 ## Next
 
-- [ ] **Status dot** (M10) — sync-drift beads on rows.
+- [ ] **Combobox** (M11) — type-to-filter pickers; adopt gpuikit's
+      `on_create` / `keep_unmatched` blur modes.
     - [x] API sketch
     - [x] Implementation (theme-baked, motion inline per AGENTS.md)
     - [x] Tests
@@ -18,8 +19,6 @@ is the first downstream consumer; its screens drive the order.
 
 ## Queue — to follow
 
-- [ ] **Combobox** (M11) — type-to-filter pickers; adopt gpuikit's
-      `on_create` / `keep_unmatched` blur modes.
 - [ ] **Command palette** (M12) — filtered actions; the matcher stays
       caller-owned.
 - [ ] **VirtualList** (M13, `data`) — thin `uniform_list` binding for commit