feat(ci): add minimal pre-commit config (opt-in) for secret detection #34

Problem

Quickstart is the entry point for users learning AI-assisted federal development. It currently lacks:

1. Pre-commit configuration (no .pre-commit-config.yaml)
2. Secret detection (gitleaks)
3. Basic file hygiene checks

However, we must avoid interfering with user workflows (see GSA-TTS/agentic-coding-playbook#42).

Proposed Solution

Add minimal, opt-in pre-commit config:

# .pre-commit-config.yaml
repos:
  - repo: https://github.com/pre-commit/pre-commit-hooks
    rev: 3e8a8703264a2f4a69428a0aa4dcb512790b2c8c  # v6.0.0
    hooks:
      - id: trailing-whitespace
      - id: end-of-file-fixer
      - id: check-yaml
      - id: check-json

  - repo: https://github.com/gitleaks/gitleaks
    rev: ee6b38352380ce52369d16b7873093c4b8bf829b  # v8.24.3
    hooks:
      - id: gitleaks

Make it opt-in:

.PHONY: install-hooks
install-hooks:  ## [OPTIONAL] Install pre-commit hooks
	pre-commit install

Document in SBX guide:

Update docs/SBX_QUICKSTART.md to show:

• How to install pre-commit in SBX
• How to run checks without installing hooks (pre-commit run --all-files)
• Why it's optional

Benefits

• ✅ Sets example of secret detection for users
• ✅ No interference (opt-in only)
• ✅ Works in SBX (via pip install)
• ✅ Aligns with playbook/patterns standards

Related

• Playbook: chore(ci): make pre-commit hooks opt-in to avoid user interference agentic-coding-playbook#42
• Patterns: Make pre-commit hooks opt-in agentic-coding-patterns#44
• Standards comparison: STANDARDS_COMPARISON.md
• Strategy doc: PRE_COMMIT_STRATEGY.md

Acceptance Criteria

• .pre-commit-config.yaml added with gitleaks + basic hooks
• make install-hooks target added (NOT in make setup)
• docs/SBX_QUICKSTART.md updated with pre-commit guidance
• README mentions pre-commit is optional
• No auto-installation in any make target

Priority: Medium
Type: Feature + Documentation