feat(nokv-workbench): add checkpoint restore workflow

[wchwawa]

Summary

• update the intrinsic NoKV Workbench skill to checkpoint and restore contract v0.4
• document terminal snapshot expiry, renew behavior, root-bound typed errors, and checkpoint registry handling
• add the restore-to-fork workflow with deterministic retry guidance and restore_manifest.json verification
• tighten PREFLIGHT around the 17-tool Workbench surface, per-agent placeholder expansion, MCP registration, and full live acceptance
• add capability and skill regression tests

Scope

This skill exposes restore-to-fork to agents. It does not promise or request in-place rollback, write fencing, SubtreeReplaced invalidation, or any FUSE behavior.

RestoreInProgress is documented as an in-flight restore-to-fork preparation or cleanup state. Agents retry the exact restore with bounded backoff.

NoKV implementation dependency: NoKV-Lab/NoKV#403

Validation

• uv run pytest -q tests/test_mcp_capability.py tests/test_skills.py: 58 passed
• uv run ruff check tests/test_mcp_capability.py
• git diff --check

The checked-in cross-repository full live E2E was rerun after rebasing this branch onto current upstream main. All 11 scenarios passed with real RustFS, nokv serve, the 17-tool Workbench MCP profile, and two LingTai agents.