feat: consolidate all new labeling rules with comprehensive tests

[ddjain]

Summary

This PR consolidates all new auto-labeling rules with comprehensive test coverage (80%+).

New Rules Added

Database Rules

• safe-migration (Issue Rule: Safe migration detection (safe-migration) #6): Detects safe migration patterns

Test Rules (Issues #7, #8, #9)

• test-only-change: Identifies test-only changes
• test-missing: Flags source changes without corresponding tests
• test-improvement: Detects test improvements/additions

Dependency Rules (Issues #10, #11, #12)

• dependency-change: Detects dependency file modifications
• new-dependency: Identifies new dependencies added
• dependency-downgrade: Flags dependency version downgrades

CI/CD Rules

• ci-change (Issue Rule: CI workflow changes (ci-change) #13): Detects CI workflow changes (GitHub Actions, GitLab CI, CircleCI, etc.)

Infrastructure Rules

• infra-change (Issue Rule: Infrastructure config changes (infra-change) #15): Identifies infrastructure config changes (Terraform, K8s, Docker, etc.)

Semantics Rules (Issues #16, #17, #18, #19)

• function-removed: Detects removed functions/classes
• new-feature: Identifies new feature additions
• non-functional-change: Flags documentation/non-code changes
• refactor: Detects refactoring/rename operations

Security Rules

• security-change (Issue Rule: Security-sensitive area changes (security-change) #20): Flags changes in security-sensitive areas (auth, crypto, JWT, OAuth)
• risky-code (Issue Rule: Risky code usage (risky-code) #21): Detects risky code patterns (eval, exec, dangerouslySetInnerHTML)

Meta Rules

• large-pr (Issue Rule: Large PR detection (large-pr) #22): Flags large PRs (>500 lines changed)
• Enhanced missing-description, no-linked-issue, work-in-progress rules

Quality Metrics

✅ All 417 tests passing
✅ 80%+ branch coverage on all rules
✅ Comprehensive edge case handling
✅ Debug mode support for all rules

Issues Closed

Closes #6, #7, #8, #9, #10, #11, #12, #13, #15, #16, #17, #18, #19, #20, #21, #22