feat: improve thumbnails, placement, and editor responsiveness

[open-pascal]

Summary

• improve thumbnail and snapshot capture flow, including the viewer frame-limiter path used during capture
• tighten spatial-grid and item placement behavior
• apply editor UI and perf cleanups across panels, sidebar tree nodes, overlays, contextual tools, and related controls
• align floorplan-panel with the split monorepo version to preserve the larger render-isolation refactor
• refresh Three to 0.184 and update related package wiring

Validation

• git diff --check
• bun --filter @pascal-app/core build
• bun --filter @pascal-app/viewer build

Notes

• bun --filter @pascal-app/editor check-types is still failing on existing repo-wide TypeScript issues in this repo, mainly R3F JSX intrinsic typings and a few sidebar strictness errors, and is not a new failure introduced by this PR