task(C4): use_pixi_renderer flag on by default with e2e proof

frontend/src/render/pixi/PixiRenderer.ts

@@ -48,6 +48,9 @@ export class PixiRenderer implements RenderAdapter {
     await this.ready;
   }
 
+  /** Task C4: true sobald setupApp fertig ist (via readyResolve gesetzt). */
+  private initialized = false;
+
   // ── Lifecycle ────────────────────────────────────────────
 
   init(canvas: HTMLCanvasElement): void {
@@ -89,6 +92,7 @@ export class PixiRenderer implements RenderAdapter {
       this.overlayLayer = overlay;
       this.app.stage.addChild(overlay);
       this.applyViewportTransform();
+      this.initialized = true;              // Task C4: fuer getDebugInfo
     });
   }
 
@@ -252,6 +256,17 @@ export class PixiRenderer implements RenderAdapter {
     return null;
   }
 
+  /**
+   * Task C4: Debug-Info für Playwright-E2E-Assertions.
+   * Ermöglicht Testabfragen wie 'wie viele Elemente sind gerendert?'
+   */
+  getDebugInfo(): { cachedElements: number; ready: boolean } {
+    return {
+      cachedElements: this.graphicsCache.size,
+      ready: this.initialized,
+    };
+  }
+
   // ── Internes ─────────────────────────────────────────────
 
   private applyViewportTransform(): void {