chore: Counter now embedded with Stimulus

Before this commit, Counter js was autonomous. Now it's registered
like a controller in Stimulus.

app/javascript/controllers/counter_controller.js

@@ -1,2 +1,61 @@
+import { Controller } from "@hotwired/stimulus"
 
+export default class extends Controller {
+  static values = { 
+    target: Number,
+    decimal: Boolean,
+    duration: { type: Number, default: 2000 }
+  }
 
+  connect() {
+    this.observer = new IntersectionObserver((entries) => {
+      entries.forEach(entry => {
+        if (entry.isIntersecting) {
+          this.animate()
+          this.observer.unobserve(this.element)
+        }
+      })
+    }, { threshold: 0.5 })
+
+    this.observer.observe(this.element)
+  }
+
+  disconnect() {
+    if (this.observer) {
+      this.observer.disconnect()
+    }
+  }
+
+  animate() {
+    const startValue = 0
+    const startTime = performance.now()
+
+    const updateCounter = (currentTime) => {
+      const elapsedTime = currentTime - startTime
+      const progress = Math.min(elapsedTime / this.durationValue, 1)
+      
+      // Easing function for smooth animation
+      const easeOutQuart = 1 - Math.pow(1 - progress, 4)
+      
+      let currentValue = startValue + (this.targetValue - startValue) * easeOutQuart
+      
+      if (this.decimalValue && this.targetValue < 10) {
+        currentValue = currentValue.toFixed(1)
+      } else {
+        currentValue = Math.floor(currentValue)
+      }
+
+      this.element.textContent = currentValue
+
+      if (progress < 1) {
+        requestAnimationFrame(updateCounter)
+      } else {
+        this.element.textContent = this.decimalValue && this.targetValue < 10 
+          ? this.targetValue.toFixed(1) 
+          : this.targetValue
+      }
+    }
+
+    requestAnimationFrame(updateCounter)
+  }
+}

app/javascript/controllers/hello_controller.js

@@ -1,7 +0,0 @@
-import { Controller } from "@hotwired/stimulus"
-
-export default class extends Controller {
-  connect() {
-    this.element.textContent = "Hello World!"
-  }
-}

app/javascript/controllers/index.js

@@ -4,8 +4,8 @@
 
 import { application } from "./application"
 
-import HelloController from "./hello_controller"
 import ShadcnTestController from "./shadcn_test_controller"
+import CounterController from "./counter_controller"
 
-application.register("hello", HelloController)
 application.register("shadcn-test", ShadcnTestController)
+application.register("counter", CounterController)