feat(KB-032): add Planning Mode for AI-assisted task creation

- Add PlanningModeModal component with interactive task planning UI
- Implement backend planning API with /api/planning endpoints
- Add PlanningSession class for managing planning state
- Integrate planning mode into dashboard with header button
- Add comprehensive tests for planning components and API routes
- Include AI agent structure for future planning automation
- Update README with Planning Mode documentation

pnpm-lock.yaml

@@ -108,6 +108,9 @@ importers:
       '@kb/core':
         specifier: workspace:*
         version: link:../core
+      '@kb/engine':
+        specifier: workspace:*
+        version: link:../engine
       '@types/multer':
         specifier: ^2.1.0
         version: 2.1.0