Summary

Adds a new "Show Dimensions" toggle to the View panel that overlays the world-space length of each axis of the selected splat's bounding box directly on the 3D viewport. Each axis label is rendered as SVG text aligned with — and offset to the outside of — the corresponding outer-silhouette edge of the box, so users can read the X/Y/Z extents at a glance while orbiting.

Implementation

• New [src/ui/bound-dimensions-overlay.ts](src/ui/bound-dimensions-overlay.ts) creates a single SVG attached to canvasContainer.dom with three <text> children (one per axis). Each frame on prerender it projects the 8 world-space corners of the splat's local bound, picks the outermost parallel edge per axis (farthest screen-space midpoint from the projected box centroid), and positions each label at that edge's midpoint, rotated to match its on-screen direction with a perpendicular offset that always points away from the box centre. Labels auto-flip 180° to stay upright.
• Behind-camera culling is done with a world-space dot product against the camera forward direction, so labels disappear cleanly when the box leaves the view frustum (rather than projecting to garbage screen coordinates).
• A 1-pixel² tie tolerance on the edge-selection score prevents frame-to-frame flicker in orthographic mode, where opposite parallel edges are exactly equidistant from the box centre.
• The "Show Dimensions" toggle is independent of "Show Bound" — users can show dimensions without the wireframe, or vice versa. State is wired through new camera.boundDimensions / camera.setBoundDimensions / camera.toggleBoundDimensions events in [src/editor.ts](src/editor.ts), defaults to false in [src/scene-config.ts](src/scene-config.ts), and round-trips via docSerialize.view / docDeserialize.view.
• Labels are styled in [src/ui/scss/tool.scss](src/ui/scss/tool.scss) with a black stroke halo (paint-order: stroke) so they remain legible against any background.
• Localized in all 9 locale files (panel.view-options.show-bound-dimensions).

Test plan

• Load a splat, select it, toggle "Show Dimensions" on — three numeric labels appear, one per axis edge.
• Orbit the camera in perspective mode — labels track the outer silhouette edges and stay upright.
• Switch to orthographic mode — labels do not flicker between frames.
• Apply translate / rotate / non-uniform scale to the splat — displayed dimensions update and match the visible wireframe extents.
• Pan the splat partially / fully off-screen — labels hide cleanly per axis.
• Toggle "Show Bound" off while "Show Dimensions" is on — labels remain visible without the wireframe.
• Save and reload the document — toggle state persists.
• Verify the new toggle string renders correctly in each locale.