[P2] Interactive results explorer

[Petsku01]

Problem

JSON artifacts hard to browse.

Tasks

• Add simple HTML viewer for results
• Filter by category, model, detector
• Side-by-side comparison mode

[Petsku01]

Triage 2026-09-14, verified against main (79aafd0): partially done.

psg/reporting/html_report.py already produces an HTML report (per-category table, categories visible). Not present: filtering (category/model/detector), side-by-side comparison mode.

Remaining work is scoped: add filter dropdowns + a compare view that joins two report JSONs on (attack_id) showing verdicts side by side.