Fix findUsages/undo/node-lookup bugs, split Viewport and Editor, share command and inspector helpers

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/ui/Theme.ts

@@ -37,12 +37,9 @@ export const Theme = {
     accentText: 0xffffff,
     text: 0xe6e8ee,
     textMuted: 0x8a90a0,
-    textDisabled: 0x5a5f6d,
     selection: 0x2b4a80,
-    override: 0xf0b13d,
     danger: 0xe0553f,
     viewport: 0x121316,
-    grid: 0x1f2126,
     gizmo: 0x4c8dff,
     /** Behavior symbols and owner links. */
     behavior: 0xb066ff,