Texture fills show in the vector tab as soon as they load (#196)

After signing out and back in, a texture fill stayed in its base
colour until something else redrew the vector tab. The texture
library is a singleton that outlives the editor. Four widgets
subscribed to it and never unsubscribed. After a new sign-in the
first loaded texture called a destroyed canvas, which threw and
stopped the loop before the vector tab heard about the image.

- TextureCanvas, TileCanvas, ShaderPreview and WorldViewport now
  unsubscribe in destroy(). This is the pattern FontPreview and
  VectorArtCanvas already use. WorldViewport leaves both the
  texture and the font library.
- FileLibrary.notifyChange catches errors per listener. A broken
  listener no longer starves the others. The error is still
  logged as "[textures] a listener failed".
- e2e 47i no longer forces a redraw. It waits up to 3 s for the
  tab to show the texture on its own.

Findings:
- The trigger was e2e module 45 (sign out, sign in), not the
  texture fill. My note in #196 that the browser showed no
  exception was wrong. The counter-check shows it clearly.

Tests:
- ./check.sh: 137 files, 2051 tests, exit 0 (before 136 / 2049)
- 2 new unit tests in tests/viewport/file-library.test.ts
- GM_STEPS=45,47 after a fresh seed: ALL PASSED, 71 checks
- Counter-check with the old source and the new check: 1 FAIL
  (shape stays #0000ff) plus the TypeError. Old FileLibrary.ts
  fails the first unit test.
- No full e2e run locally. The check count is unchanged.

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

src/editor/texture/TextureCanvas.ts

@@ -136,6 +136,7 @@ export class TextureCanvas extends Widget {
   private collision = false;
   /** 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;
 
   constructor(private readonly state: EditorState) {
     super();
@@ -159,7 +160,13 @@ export class TextureCanvas extends Widget {
       this.redraw();
     });
     // A picture arrives asynchronously; until then there is nothing to fit the view to.
-    textureLibrary.onChange(() => this.redraw());
+    this.stopPictures = textureLibrary.onChange(() => this.redraw());
+  }
+
+  /** The library outlives a signed-out editor; a stale listener would redraw destroyed graphics. */
+  override destroy(options?: Parameters<Widget['destroy']>[0]): void {
+    this.stopPictures();
+    super.destroy(options);
   }
 
   override measure(): Size {