Dragging previews once per frame instead of on every move (#213)

Scene view, texture tab and graph called state.preview() on every
pointer move. Each call rebuilds panels, the editor run and generated
images, so a drag in a busy project cost up to 34 ms per move. The
model is still written on every move. Only the preview now waits for
the next frame.

- New FramePreview in src/editor/framePreview.ts. request() goes into
  the move handler, cancel() into the release. The rule lives in one
  place instead of six copies.
- Scene view: object drag, polygon corners and tilemap strokes use it.
- Texture tab: frames, slice edges and collision corners use it.
- Graph: nodes, groups and comments use it through GraphDrags. That
  covers the state machine, shader and particle tabs as well.
- Vector art is unchanged. Its frame already writes the model since
  #129.

Findings:
- The texture tab paid twice per move (232 project events for 120
  moves). Pixi sends a second pointer event 4 to 8 ms after each real
  move as a hover update. It now lands in the same frame for free.
- Inspector scrubbing and gradient stop dragging still preview on
  every input. Both lie outside the three canvases of the issue.

Measured with a throwaway probe, 120 moves at 8 ms, 120 extra objects:
scene 26.2 -> 18.5 ms/move, texture 34.2 -> 17.9, graph 28.8 -> 17.0.
Project events dropped from 120/232/119 to 48/48/41.

Tests:
- ./check.sh: 147 files, 2204 tests, exit 0 (before 146 / 2199).
- 5 new unit tests in tests/editor/frame-preview.test.ts, including
  the real GraphDrags. Counter-checks (direct preview in the graph,
  no cancel on release, one key per name) each fail the expected test.
- e2e 1-16,29,31,36,37,39-43: 708 checks passed.
- e2e 1-16,26,28: 634 checks passed.
- No new e2e check, the check sum stays at 1314.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/editor/texture/TextureCanvas.ts

@@ -33,6 +33,7 @@ import {
 } from '../polygonEdit';
 import { dashedLine } from '../../viewport/symbols';
 import { textureLibrary } from '../../viewport/TextureLibrary';
+import { FramePreview } from '../framePreview';
 import type { EditorState } from '../state';
 import { drawChecker } from './checker';
 import { SheetCanvas } from './SheetCanvas';
@@ -118,9 +119,11 @@ export class TextureCanvas extends SheetCanvas<TextureAsset> {
   /** The outline a click adds corners to; for another frame, or one gone, the frame's last one. */
   private active = { frameId: '', index: -1 };
   private readonly stopPictures: () => void;
+  private readonly perFrame: FramePreview;
 
   constructor(private readonly state: EditorState) {
     super();
+    this.perFrame = new FramePreview(state, 'texture-drag');
     this.content.addChild(this.image, this.overlay, this.labelLayer);
 
     state.on('project', () => this.redraw());
@@ -344,7 +347,7 @@ export class TextureCanvas extends SheetCanvas<TextureAsset> {
     const frame = corner && this.frame(corner.frameId);
     if (!corner || !frame) return;
     setFrameCollision(frame, corner.outlines);
-    this.state.preview();
+    this.perFrame.request();
   }
 
   private startDrag(
@@ -424,10 +427,11 @@ export class TextureCanvas extends SheetCanvas<TextureAsset> {
         frame,
         normalizeFrameRect(dragFrame(drag.start, drag.handle, dx, dy), asset.width, asset.height),
       );
-    this.state.preview();
+    this.perFrame.request();
   }
 
   protected release(): void {
+    this.perFrame.cancel();
     const corner = this.corner;
     this.corner = null;
     const frame = corner && this.frame(corner.frameId);