Spec1: minimal qualitative figure util (score curve vs GT)

[jinmang2]

Part of #16 (Spec 1 — Foundation).

Scope

• One per-frame anomaly-score curve with GT anomaly-region shading. Liveness proof for the pipeline; full suite is Spec 3 ([Epic] WSVAD comparison framework: multi-backbone matrix + HF-style serving + streaming inference #16).

Done when

• Given pipeline scores + a GT interval, produces a saved figure.

[jinmang2]

Consolidated into PR #22 (tracked in the PR checklist) to keep management to PR + Epic only. Code for done items is in PR #22; remaining items live in the PR's Spec-1 checklist.