feat(KB-048): add collapsible list sections to dashboard

- Add section expansion state management with localStorage persistence
- Update section headers with chevron toggle controls
- Implement conditional task row rendering based on section state
- Add Expand All / Collapse All toolbar controls
- Add CSS styles for chevron rotation animation and section headers
- Add comprehensive tests for collapsible section behavior

packages/engine/src/restart.integration.test.ts

@@ -351,7 +351,7 @@ describe("In-review merge handling after restart", () => {
     } as any);
 
     await expect(aiMergeTask(store, "/tmp/root", "KB-055")).rejects.toThrow(
-      "AI merge failed for KB-055: merge agent crashed",
+      "AI merge failed for KB-055: all 3 attempts exhausted",
     );
 
     // Should have attempted git reset --merge cleanup