feat(openagent): restore verified checkpoints - #197

Summary

• expose durable checkpoint IDs with OpenAgent run details
• add a desktop restore command and typed frontend API
• permit only completed before-mutation snapshots with matching after-state evidence
• preflight current SHA-256 state, checkpoint payload digests, symlinks, extra directory entries, and attached-root containment
• block active-run restore and conflicts caused by later user edits
• add successful restore and conflict-preservation regression tests

Validation

• npm run build
• npm run lint (2 pre-existing warnings, 0 errors)
• npm run test:image
• version, release, and model catalog checks
• git diff --check

Rust formatting, clippy, and tests run in repository CI.