Add pluggable verifier interface for skill promotion

[nutstrut]

Motivation

• Introduce a new verified_skills operating mode to gate automatic skill promotion with pluggable verifiers.
• Provide a safe verification fallback so skill evolution can run even if verifier configuration fails.

Mode comparison

Mode	GPU Required	Cloud Required	Verification	Auditability
skills_only	No	No	None	Existing skill metadata
verified_skills	No	No by default	Pluggable verifier	Verification metadata + optional receipts
rl	No	Yes	Existing RL evaluation	Existing training artifacts
madmax	No	Yes	Existing training path	Existing training artifacts

Description

• Add a verification subsystem under metaclaw/verification with a VerifierInterface, VerificationResult, and implementations: LocalVerifier, NullVerifier, RemoteHTTPVerifier, and SettlementWitnessVerifier, plus a factory with build_verifier/build_verifier_safe helpers.
• Add VerificationConfig and wire a verification field into MetaClawConfig and _DEFAULTS in config_store, and expose config parsing in ConfigStore.to_metaclaw_config and describe.
• Integrate verifier into the FastAPI proxy (metaclaw/api_server.py) by building a safe verifier, constructing verification packets for evolved skills, attaching verification metadata, auditing rejected/indeterminate promotions, and skipping promotion unless verifier rules permit it.
• Add verified_skills to the CLI and interactive SetupWizard, treat it similar to skills_only in launcher and environment setup, and update README.md with mode docs and config examples.
• Extend SkillManager to persist and load optional metadata.json alongside SKILL.md so verifier metadata is stored with skills.
• Add unit tests in tests/test_verification.py covering NullVerifier, LocalVerifier behavior, and factory/fallback selection.

Testing

• Ran the new unit tests with pytest -q tests/test_verification.py and all tests passed.

• Verified the verification factory fallback by creating a MetaClawConfig with a bad verifier and asserting build_verifier_safe returns a NullVerifier (test passed).

• Exercised LocalVerifier cases in unit tests covering fail/duplicate/indeterminate/pass verdicts (all assertions succeeded).

• Focused verifier/runtime tests passed:

• pytest -q tests/test_verification.py tests/test_memory_system.py tests/test_runtime_state.py

• Result: 537 passed

---

Codex Task