朱子纯 / erp-workflow-plugin

…it trailer, verify-fail guidance

- Add feature-spec (brainstorm+plan merged, phase switch for backend/frontend)
- Overwrite feature-tdd with dual-phase support (path guards, test dispatch, commit trailers)
- Overwrite feature-review with verify+review merged, both reviewer agents, phase-driver callback, 5-round cap
- Delete 8 superseded skills: feature-{brainstorm,plan,verify} + fe-feature-{brainstorm,plan,tdd,verify,review}