feat: require explicit project agents

[whoisasx]

Summary

• require explicit worker/orchestrator agent resolution before spawning sessions; no daemon AO_AGENT fallback for those spawn paths
• add project creation agent selection in the desktop sidebar, persist worker/orchestrator config, then auto-start and navigate to the orchestrator
• update project settings, CLI help/docs, and tests for explicit project role agents

Reviewer agent behavior is intentionally unchanged.

Tests

• (cd backend && go test ./internal/session_manager ./internal/service/session ./internal/daemon ./internal/cli)
• (cd frontend && pnpm typecheck)
• (cd frontend && pnpm vitest run --config vite.renderer.config.ts src/renderer/components/ProjectSettingsForm.test.tsx src/renderer/components/Sidebar.test.tsx)
• git diff --check