feat: improve thumbnails and reduce editor rerenders

[open-pascal]

Summary

• clean thumbnail captures by hiding scans and guides
• add post-processed thumbnail generation with snapshot camera data and wall cutout support
• reduce editor rerenders by memoizing the viewer scene/canvas and narrowing subscriptions
• optimize site tree updates and delete interactions

Validation

• git diff --check
• biome check on touched files
• repo-wide check-types is currently failing on existing baseline issues, so it was not a clean gating signal for this PR