feat(collaboration): emulate codex plan/orchestrator behavior

[iam-brain]

Summary

• add codex-style collaboration profile emulation for plan and orchestrator agents, including mode-aware instruction injection and collaboration headers
• add runtime collaboration gates (collaborationProfile, orchestratorSubagents, collaborationToolProfile) with codex-mode defaults and env/config wiring
• manage an orchestrator agent file under ~/.config/opencode/agents and gate visibility by effective collaboration mode, with installer + test coverage
• update dependency-review workflow to skip cleanly when repository dependency graph support is unavailable

Verification

• npm run typecheck
• npm test
• npm run build