Implement agent-native Shipgate protocol

[pengfei-threemoonslab]

Summary

• Promote shipgate check and agent_result_v1 as the canonical agent-facing protocol across Codex, Claude Code, and Cursor
• Add deterministic policy discovery, repair-loop handling, human-stop boundaries, and a read-only MCP shipgate.check tool
• Update docs, adoption kits, examples, goldens, and renderer outputs to match the new protocol

Testing

• Added and updated unit and integration coverage for agent protocol behavior, renderers, static-only guarantees, and GitHub Action outputs
• Regenerated schema and golden fixtures to verify the new JSON contract end to end