[Ops][Slice] Visual audit pack workflow

[Prekzursil]

Parent: #39

Scope

Add visual audit workflow for desktop/live workflow evidence packs.

Acceptance Criteria

• docs/VISUAL_AUDIT_RUNBOOK.md defines visual-pack naming and baseline contract.
• tools/compare-visual-pack.ps1 generates compare report JSON with changed/new/missing breakdown.
• .github/workflows/visual-audit.yml supports manual run by run_id and uploads compare artifacts.

Evidence

• pwsh ./tools/compare-visual-pack.ps1 -BaselineDir <baseline> -CandidateDir <candidate> -OutputPath <output>