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/viewport/FileLibrary.ts

@@ -30,7 +30,13 @@ export abstract class FileLibrary<T> {
 
   /** Runs the listeners: something they draw from has changed without a file arriving here. */
   notifyChange(): void {
-    for (const listener of this.listeners) listener();
+    // One listener that throws must not keep the file from the ones after it (#196).
+    for (const listener of this.listeners)
+      try {
+        listener();
+      } catch (error) {
+        console.error(`[${this.tag}] a listener failed`, error);
+      }
   }
 
   protected abstract fetchFile(url: string, file: string): Promise<T>;