feat: add per-project bash command allowlist system

Implement hierarchical command security with project and org-level configs:

WHAT'S NEW:
- Project-level YAML config (.autocoder/allowed_commands.yaml)
- Organization-level config (~/.autocoder/config.yaml)
- Pattern matching (exact, wildcards, local scripts)
- Hardcoded blocklist (sudo, dd, shutdown - never allowed)
- Org blocklist (terraform, kubectl - configurable)
- Helpful error messages with config hints
- Comprehensive documentation and examples

ARCHITECTURE:
- Hierarchical resolution: Hardcoded → Org Block → Org Allow → Global → Project
- YAML validation with 50 command limit per project
- Pattern matching: exact ("swift"), wildcards ("swift*"), scripts ("./build.sh")
- Secure by default: all examples commented out

TESTING:
- 136 unit tests (pattern matching, YAML, hierarchy, validation)
- 9 integration tests (real security hook flows)
- All tests passing, 100% backward compatible

DOCUMENTATION:
- examples/README.md - comprehensive guide with use cases
- examples/project_allowed_commands.yaml - template (all commented)
- examples/org_config.yaml - org config template (all commented)
- PHASE3_SPEC.md - mid-session approval spec (future enhancement)
- Updated CLAUDE.md with security model documentation

USE CASES:
- iOS projects: Add Swift toolchain (xcodebuild, swift*, etc.)
- Rust projects: Add cargo, rustc, clippy
- Enterprise: Block aws, kubectl, terraform org-wide
- Custom scripts: Allow ./scripts/build.sh

PHASES:
✅ Phase 1: Project YAML + blocklist (implemented)
✅ Phase 2: Org config + hierarchy (implemented)
📋 Phase 3: Mid-session approval (spec ready, not implemented)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

requirements.txt

@@ -9,6 +9,7 @@ psutil>=6.0.0
 aiofiles>=24.0.0
 apscheduler>=3.10.0,<4.0.0
 pywinpty>=2.0.0; sys_platform == "win32"
+pyyaml>=6.0.0
 
 # Dev dependencies
 ruff>=0.8.0