fix: improve text sharpness on zoom with tighter buckets and reliable init

Fix text staying blurry on zoom by ensuring the first setZoomBucket call
always applies (PixiJS v8 defaults to auto-resolution which skipped the
initial bucket=1 assignment), listening on both 'moved' and 'zoomed'
viewport events, and tightening bucket thresholds from 6 to 9 levels.

frontend/src/canvas/sprites/TextCore.ts

@@ -35,6 +35,7 @@ export class TextCore {
   private _lastWordWrapWidth: number;
   private _lastLineHeightMultiplier: number;
   private _zoomBucket = 1;
+  private _zoomBucketApplied = false;
 
   get measuredWidth(): number {
     return this.pixiText.width;
@@ -81,8 +82,11 @@ export class TextCore {
    * Only re-rasterizes when the bucket actually changes.
    */
   setZoomBucket(bucket: number): void {
-    if (bucket === this._zoomBucket) return;
+    // Always apply on first call (resolution starts as null/auto in PixiJS v8).
+    // After that, skip if bucket hasn't changed.
+    if (this._zoomBucketApplied && bucket === this._zoomBucket) return;
     this._zoomBucket = bucket;
+    this._zoomBucketApplied = true;
     this.pixiText.resolution = bucket;
   }
 

frontend/src/canvas/textSharpness.ts

@@ -21,11 +21,14 @@ import { StickySprite } from './sprites/StickySprite';
  * Fewer buckets = fewer re-rasterizations = better perf.
  */
 export function getTextZoomBucket(scale: number): number {
-  if (scale < 0.4) return 0.5;
-  if (scale < 0.75) return 0.75;
-  if (scale < 1.25) return 1;
-  if (scale < 1.75) return 1.5;
-  if (scale < 2.5) return 2;
+  if (scale < 0.3) return 0.25;
+  if (scale < 0.5) return 0.5;
+  if (scale < 0.8) return 0.75;
+  if (scale < 1.1) return 1;
+  if (scale < 1.4) return 1.25;
+  if (scale < 1.8) return 1.5;
+  if (scale < 2.2) return 2;
+  if (scale < 3.0) return 2.5;
   return 3;
 }