[P2] Add JSON/HTML/PDF Report Contract Tests

[barvhaim]

Roadmap Item 14: Add JSON/HTML/PDF Report Contract Tests

Priority: P2
Area: Reporting
References: src/threatxtension/core/report_generator.py,
src/threatxtension/api/main.py

Reports should be stable artifacts for security teams. They need contract coverage so
future analyzer changes do not silently break report fields.

Scope:

• Define a canonical report data model.
• Add snapshot-style tests for JSON and rendered report metadata.
• Ensure PDF generation handles missing optional sections.
• Include analyzer health and normalized findings in report output.

Acceptance criteria:

• Report generation works for complete, partial, and failed scans.
• Missing VirusTotal, Chrome Stats, or LLM data does not crash report generation.
• Report field names are documented and tested.

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Created from docs/roadmap.md.