Add Codex Computer Use runtime setup

[HomunculusLabs]

Summary

• add first-class Codex Computer Use setup/status UX and runtime launchability checks
• resolve Codex app-managed Computer Use plugin .mcp.json into one-turn app-server MCP overrides
• add opt-in Codex app-server diagnostics and method-aware timeout messages

Validation

• .agents/skills/rpce-contribution-check/scripts/preflight.sh push against upstream/main
• make dev-lint
• make dev-test
• make dev-swift-build PRODUCT=RepoPrompt

Note: non-disruptive make dev-smoke could not run locally because RepoPrompt CE was not running/MCP-connectable.

[HomunculusLabs]

This is NOT READY to be merged. Requires a signed build in order to test.