[codex] replay checkpoints from project storage

[salim4n]

Closes #48

What changed

• Added a native checkpoint inference command that validates checkpoint payloads from local project storage and writes a completed inference run with metrics and trace data.
• Added a Studio checkpoint action to run inference and select the resulting run/episode so replay and reward debugger panels open immediately.
• Surfaced native checkpoint inference errors through the existing Studio alert.
• Covered success and missing-payload error paths in React and Tauri tests.

Validation

• bun test apps/studio/src/App.test.tsx
• bun run --cwd apps/studio typecheck
• cargo test --manifest-path apps/studio/src-tauri/Cargo.toml
• bun run ci