feat(acp): Add OpenClaw Gateway bridge through openclaw acp

[matdev83]

feat(acp): Add OpenClaw Gateway bridge through openclaw acp

Related: https://docs.openclaw.ai/tools/acp-agents

Current architecture / implementation constraints

Treat this as an external agent-runtime connector/bridge, not as an inference backend and not as a second ACP implementation.

• Reuse connector-support/acp as the single ACP protocol/session/tool/stream implementation (refactor: deduplicate ACP runtime #242).
• Package the OpenClaw Gateway bridge under connectors/ using the executable backend-plugin/process-host architecture (feat: add executable backend connector plugins #208).
• Declare execution_class: agent_runtime; feat(routing): agent-runtime execution composition safety #337 allows direct routes while protecting unsafe weighted/parallel/thinker/failover composition by default.
• Keep OpenClaw-specific code limited to gateway launch/connection/configuration/discovery/lifecycle behavior and any genuinely OpenClaw-specific ACP adaptation.
• Do not duplicate generic ACP message mapping, tool-event handling, cancellation, structured error propagation, process supervision, or session mechanics.
• Preserve optional dependency isolation and use connector-local contract/parity/process-tree tests plus generic ACP TCK coverage.

No dedicated Kiro SDD or implementation PR exists yet.