Preview a sprite at the end of its inspector, placed or as an asset

A sprite's inspector listed its rows but never showed what they add up
to. The picture, its frame, nine-slice, tint and shader could only be
judged in the scene, often far from the object being edited.

- SpritePreview draws the sprite through syncSpriteMesh, the function
  the scene draws it with. Slices, padding, tint and shader come out
  the same without a second path. syncSpriteMesh now takes only the
  three fields of a DrawItem it reads.
- The subject is resolved by previewPicture from the Shader tab, so a
  placed sprite shows its own overrides.
- previewFit is the rule for size and place: whole device pixels per
  unit from 1 on, at most 8, and the corner on a whole device pixel.
  Pixel art stays sharp. A sprite larger than the group shrinks freely.
- A shader with a Time node keeps the preview redrawing once a frame
  while it is on screen. A folded group or a hidden panel stops it.
- New test hook __gm.inspectorSpritePreview().

Finding: the preview redrew on a model change in a microtask at first.
A drawn picture whose revision moved on is retried once, in a
microtask queued by the scene's synchronous redraw. That retry ran
before the preview had let go, and the old pixel art sheet stayed
waiting (e2e 48l-iii read waiting [1,1,1]). The preview now redraws
at once on a model change, as the scene does.

Tests:
- unit: 238 files, 3592 tests (+5 in preview-fit.test.ts), and the
  group list of a placed sprite in sections.test.ts ends in PREVIEW
- e2e 48: ALL PASSED, 47 checks (+2: 48l-i asset preview with
  the frame, 48l-iii placed preview with its shader values)
- counter-checks: without whole-pixel zoom 2 unit tests fail; with
  the microtask redraw 48l-iii fails with waiting [1,1,1]

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

src/editor/debug/uiHooks.ts

@@ -18,6 +18,7 @@ import { generalSettings, keepGeneralSettings } from '../generalSettings';
 import { currentGroupDialog } from '../panels/GroupNameDialog';
 import { currentSoundPicker } from '../sound/SoundPicker';
 import { rectOf, textProbe } from '../textProbe';
+import { SpritePreview } from '../inspector/SpritePreview';
 import { currentImagePicker } from '../texture/ImagePicker';
 import type { UsersPane } from '../users/UsersPane';
 import { Color, type ColorSource, type Container, Text } from 'pixi.js';
@@ -167,6 +168,21 @@ export function uiHooks({ app, state, editor }: HookContext) {
       return (last ? hits.at(-1) : hits[0]) ?? null;
     },
     inspectorField: fieldOf,
+    /** A sprite's preview in the inspector, scrolled into view: where its picture is drawn, on screen. */
+    inspectorSpritePreview: () => {
+      let preview: SpritePreview | null = null;
+      const walk = (node: Container): void => {
+        if (node instanceof SpritePreview) preview = node;
+        else for (const child of node.children) walk(child);
+      };
+      walk(inspector);
+      const found = preview as SpritePreview | null;
+      if (!found) return null;
+      inspector.reveal(found);
+      const at = found.getGlobalPosition();
+      const { x, y, w, h } = found.drawn;
+      return { x: at.x + x, y: at.y + y, w, h, animates: found.animates };
+    },
     /** The mark in front of the row named `label` – what a variable, a field or a port is dragged by (#310). */
     inspectorMark: (label: string, last = false) => {
       const mark = besideOf(label, last, -1);