fix(scene): normalize indexed filenames on read

[YOMXXX]

Summary

• normalize filenames loaded from .metadata/scene_index.json
• prevent stale or malformed scene metadata from feeding path segments to downstream readers/navigation
• add a regression test for ../../secret.md metadata filenames

Why

scene_index.json is normally generated by syncSceneIndex(), but stale/corrupt metadata can be consumed by persona generation and recall navigation. Normalizing on read keeps downstream code operating on safe single-segment scene filenames.

Tests

• npm test -- src/core/scene/scene-index.test.ts
• npm test
• npm run build
• git diff --check

[Maxwell-Code07]

Thanks for your attention! We’ll review this and get back to you as soon as possible.