Plugin: add autonomous Codex worker tools

[Yehonal]

Summary

Add experimental agent-callable worker tools on top of the Codex app-server plugin so OpenClaw can orchestrate a configured Codex worker without relying on manual /cas_* interaction.

What this adds

• codex_workers_describe_endpoints
• codex_workers_list_threads
• codex_workers_run_task
• codex_workers_read_thread_context

Why

The current /cas_* flow is still useful for humans, but OpenClaw also benefits from a tool-callable surface for autonomous orchestration.

This PR keeps the manual CAS UX intact while exposing a separate agent-oriented interface.

Scope

This version is intentionally standalone against main:

• it works with the current single-endpoint plugin configuration
• it does not require multi-endpoint support to be useful
• multi-endpoint support would make the feature more powerful, but is not a prerequisite for this PR

Notes

• The new tools talk directly to the configured Codex app-server transport.
• /cas_* commands are unchanged and remain the human-facing/manual fallback.
• Docs added in docs/autonomous-worker-tools.md.
• The feature is still marked experimental.

Validation

• npx tsc -p tsconfig.json
• npx vitest run index.test.ts src/client.test.ts src/format.test.ts

[Yehonal]

Superseded by integration/yehonal-cas-stack reconciliation; closing this PR to avoid duplicate history.