Implement builtin_profiles.rs with 5 standard profiles (planner, coder, reviewer, tester, researcher), each with appropriate system prompts, tool permissions, and security scopes. Add resolve_profile() function that checks project-level, user-level, and built-in profiles in order, with cycle detection for inheritance chains. Verification: - All 20 profile tests pass (built-in resolution, project/user override, inheritance) - All existing tests still pass Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>