feat(openagent): harden restore recovery

[smshagor-dev]

Summary

• persist checkpoint restore audit events and expose them through the typed run-details API
• verify checkpoint payloads before mutation and attempt compensating rollback after a partial restore failure
• recover abandoned active steps and restore events on startup
• mark restored runs as requiring validation and report when validation cannot run

Validation

• npm run lint (passes with 2 pre-existing React hook warnings)
• npm run build
• git diff --check
• Rust format/build/tests delegated to GitHub Actions because this runner has no Rust toolchain

Scope notes

• release version remains 3.0.1
• true filesystem transactions, fully handle-based symlink race protection, and the strong OS process sandbox remain explicit follow-up work