feat(executor): add result verification framework

[KouweiLee]

Summary

• add the common robonix/service/verifier/verify capability contract with call_id and opaque args_json
• add Executor-owned verification rules with exact provider matching before contract fallback
• verify successful sync and async capability results before publishing the single terminal RTDL event
• fail closed on rejected, unavailable, malformed, or timed-out verifier responses
• share the immutable verification policy across parallel plan branches with Arc

Follow-up work

• implement SceneVerifier under services/verifiers/
• implement VlmVerifier under services/verifiers/
• stabilize verifier-specific args_json conventions after both implementations exist
• add deployment verification rules and verifier-backed Webots and ranger-car end-to-end scenarios

[KouweiLee]

Implementation split / next steps:

1. This PR provides the shared Verify contract and Executor-owned verification pipeline only.
2. Add SceneVerifier under services/verifiers/ and define its verifier_args parsing. @1mujue
3. Add VlmVerifier under services/verifiers/, including explicit camera provider selection. @KouweiLee
4. After both implementations stabilize, tighten the args_json convention and add verifier-backed Webots and ranger-car end-to-end coverage.

[1mujue]

Commits follow the code conduct of Robonix.