feat: Add Docker testing, enhanced audit output, and v3.3.0 improvements

[wz-gsa]

Summary

This release modernizes Caulking with comprehensive local testing infrastructure, improved documentation, and enhanced audit capabilities for federal compliance.

Features

• Add Docker-based local testing (Dockerfile, docker-compose.yml)
• Add multi-distro testing (Ubuntu, Debian, Alpine) via Docker
• Add CI simulation and upgrade path testing via Docker
• Add make status for quick health checks
• Add verification ID to audit output for compliance (NIST AU-10)
• Add platform info (OS/arch) to audit output
• Add caulking version to audit output

Bug Fixes

• Fix find argument order in check_repos.sh (-maxdepth before -name)
• Improve error handling for Homebrew gitleaks installation

Documentation

• Add "What gets blocked" section documenting gitleaks patterns and filename denylist
• Add Linux installation instructions to README
• Add pre-push scanning flow documentation in hook-wrapper.sh
• Add Windows/WSL guidance
• Add upgrading instructions
• Clarify SKIP=gitleaks limitations (only bypasses content scanning, not denylist)

Code Quality

• DRY refactor: Centralize XDG paths in lib.sh (caulking_export_paths)
• Remove unused color variables from pretty.sh
• Update pre-commit-shfmt to v3.13.1-1
• Update actionlint to v1.7.12

Testing

• Add test_prepush_ref_parsing.sh (5 test cases)
• Add test_skip_gitleaks.sh (3 test cases)
• Add test_gitleaks_missing.sh
• Add test_local_hook_chain.sh (3 test cases)

Enhanced Audit Output

The make verify audit box now includes compliance-friendly information:

+---------------------------------------------------------+
| Caulking Audit [OK]                                     |
+---------------------------------------------------------+
| - All checks passed.                                    |
|                                                         |
| - Verification ID : caulk-20260429-221622-bb9a4a92      |
|                                                         |
| - User            : username                            |
| - Host            : hostname                            |
| - Platform        : macOS 15.0 (arm64)                  |
| - Date            : 2026-04-29T22:16:22Z                |
|                                                         |
| - caulking        : 3.3.0                               |
| - prek            : prek 0.3.11                         |
| - gitleaks        : 8.30.1                              |
| ...                                                     |
+---------------------------------------------------------+

Docker Testing Commands

For local Linux testing (no CI required):

make docker-test     # Fast Ubuntu tests
make docker-full     # Full Ubuntu pipeline
make docker-debian   # Debian 12 compatibility
make docker-alpine   # Alpine/musl compatibility  
make docker-ci       # CI environment simulation
make docker-fresh    # Error handling (no gitleaks)
make docker-upgrade  # Upgrade path testing
make docker-all      # Run everything

Testing

• make test passes on macOS
• make docker-test passes on Linux (Ubuntu)
• make docker-full passes (install + verify + test)
• make docker-debian passes
• make docker-alpine passes