fix: improve demo performance and fix broken component animations

- Add IntersectionObserver-based visibility pausing to AnimationLoopService
  (registerWithElement) so canvas components auto-pause when off-screen
- Fix voronoi-mesh: increase step size, add cell cache with invalidation
- Fix particle-field: replace O(n²) connections with spatial grid partitioning
- Fix ambient-light: remove GPU-killing blur filters, use inset -20% instead
- Tune demo: reduce particle/seed counts, remove always-on floating-layers
- Fix celebration components: move effect() inside afterNextRender so canvas
  is ready, pass [active]="true", render as fixed overlays instead of inline
- Fix one-shot text effects (typewriter, scramble-reveal, counter-rollup):
  defer animation until element is visible via IntersectionObserver

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/components/fl-gradient-mesh/fl-gradient-mesh.component.ts

@@ -62,7 +62,7 @@ export class FlGradientMeshComponent {
       }
 
       const id = `gradient-mesh-${Math.random().toString(36).slice(2)}`;
-      this.loopCleanup = this.animationLoop.register(id, (delta) => this.tick(delta));
+      this.loopCleanup = this.animationLoop.registerWithElement(id, this.el.nativeElement, (delta) => this.tick(delta));
     });
 
     this.destroyRef.onDestroy(() => {