feat: add comprehensive State Management V2 documentation
- Add complete V2 decorators guide (state-management-v2.md, 38KB)
- @ComponentV2, @Local, @Param, @Event
- @ObservedV2, @Trace, @Computed, @Monitor
- @Provider/@Consumer for cross-level sync
- V1 vs V2 comparison and migration guide
- Best practices and troubleshooting
- Add 9 practical V2 code examples (state-management-v2-examples.ets, 13KB)
- Basic components, nested objects, parent-child communication
- Computed properties, monitors, providers/consumers
- Real-world patterns: forms, todo lists, collections
- Update SKILL.md with V2 decorators reference table
- Source: Official OpenHarmony documentation (API 12+)
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