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>

demo/package.json

@@ -0,0 +1,25 @@
+{
+  "name": "flair-elements-ui-demo",
+  "version": "0.1.0",
+  "private": true,
+  "scripts": {
+    "start": "ng serve --port 4203",
+    "build": "ng build"
+  },
+  "dependencies": {
+    "@angular/animations": "^19.1.0",
+    "@angular/common": "^19.1.0",
+    "@angular/compiler": "^19.1.0",
+    "@angular/core": "^19.1.0",
+    "@angular/platform-browser": "^19.1.0",
+    "@angular/platform-browser-dynamic": "^19.1.0",
+    "@sda/flair-elements-ui": "file:../dist",
+    "@sda/base-ui": "file:../../base-ui/dist"
+  },
+  "devDependencies": {
+    "@angular-devkit/build-angular": "^19.1.0",
+    "@angular/cli": "^19.1.0",
+    "@angular/compiler-cli": "^19.1.0",
+    "typescript": "~5.5.0"
+  }
+}