feat(algorithms): add live metrics to algorithm pages

Each algorithm page shows its numbers with app-metrics.
FpsCounter publishes a rate every 500 ms, not every frame.
Fractal 2D reset now also resets the zoom slider.

src/app/shared/fps-counter.ts

@@ -0,0 +1,30 @@
+import {signal} from '@angular/core';
+
+/** Counts ticks and publishes a rate a few times per second, so the display never costs frame time. */
+export class FpsCounter {
+  readonly fps = signal(0);
+  private ticks = 0;
+  private windowStart = 0;
+
+  constructor(private readonly intervalMs = 500) {}
+
+  tick(now: number = performance.now()): void {
+    if (this.windowStart === 0) {
+      this.windowStart = now;
+      return;
+    }
+    this.ticks++;
+    const elapsed = now - this.windowStart;
+    if (elapsed >= this.intervalMs) {
+      this.fps.set(Math.round(this.ticks * 1000 / elapsed));
+      this.ticks = 0;
+      this.windowStart = now;
+    }
+  }
+
+  reset(): void {
+    this.ticks = 0;
+    this.windowStart = 0;
+    this.fps.set(0);
+  }
+}