docs: reorganize documentation to match CLAUDE.md standards

Reorganize and consolidate documentation following CLAUDE.md conventions:

1. Move test helpers documentation:
   - Moved: test/utils/TEST_HELPERS_README.md → docs/test-helpers.md
   - Fixes location (should be in docs/) and naming (lowercase-hyphenated)
   - Complies with standard repo documentation structure

2. Consolidate CI testing documentation:
   - Removed: docs/ci-testing-tools.md (315 lines, redundant)
   - Kept: docs/package-testing-guide.md (comprehensive, authoritative)
   - ci-testing-tools.md was 70% duplicate of package-testing-guide.md
   - Single source of truth for CI testing workflows

3. Fix emoji usage to match CLAUDE.md standards:
   - Replaced 🚨 with plain text "CRITICAL"
   - Replaced ✅ with ✓ (colored text symbol for terminal compatibility)
   - Replaced ❌ with ✗ (colored text symbol for terminal compatibility)
   - Aligns with Socket Logger standards (yoctocolors-cjs)

Changes ensure:
- Documentation follows canonical CLAUDE.md location/naming standards
- Emoji usage matches @socketsecurity/lib/logger LOG_SYMBOLS
- No redundant documentation maintained
- Clear hierarchy and single source of truth

Files affected:
- test/utils/TEST_HELPERS_README.md → docs/test-helpers.md (moved)
- docs/ci-testing-tools.md (removed)
- docs/package-testing-guide.md (emoji fixes applied)

Author: jdalton