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>

tests/editor/sections.test.ts

@@ -351,6 +351,7 @@ describe('the groups of the inspector', () => {
       '[TRANSFORM]',
       '[EDITOR OFFSET (SCENE VIEW ONLY)]',
       '[PROPERTIES]',
+      '[PREVIEW]',
     ]);
   });