test: add test coverage for identify_tools.py HTML report functions

Add 25 unit tests covering:
- save_report_html: file creation, HTML structure, content validation
- _generate_html_report pct calculation: zero total, equal/varying distributions
- _generate_candidate_rows: empty list, single/multiple candidates
- _generate_module_cards: empty list, single module, 12-item limit
- Edge cases: empty report, special characters, long paths, coupled-only

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

Author: aledlie