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/angular.json

@@ -0,0 +1,34 @@
+{
+  "$schema": "./node_modules/@angular/cli/lib/config/schema.json",
+  "version": 1,
+  "newProjectRoot": "projects",
+  "projects": {
+    "demo": {
+      "projectType": "application",
+      "root": "",
+      "sourceRoot": "src",
+      "prefix": "app",
+      "architect": {
+        "build": {
+          "builder": "@angular-devkit/build-angular:application",
+          "options": {
+            "outputPath": "dist",
+            "index": "src/index.html",
+            "browser": "src/main.ts",
+            "polyfills": ["zone.js"],
+            "tsConfig": "tsconfig.app.json",
+            "styles": ["src/styles.scss"],
+            "scripts": [],
+            "preserveSymlinks": true
+          }
+        },
+        "serve": {
+          "builder": "@angular-devkit/build-angular:dev-server",
+          "options": {
+            "buildTarget": "demo:build"
+          }
+        }
+      }
+    }
+  }
+}