feat: add fancy animation to Mark as Read button

- Icon spins 360° with bounce effect (scale up during spin)
- Button background changes to vibrant green gradient (#10b981)
- Green pulsing box-shadow effect on activation
- Button scales up slightly on click for emphasis
- Holds green state for 1.5 seconds
- Smoothly fades to gray after animation
- Final state is gray button to indicate marked status
- Uses cubic-bezier easing for modern, smooth feel
- Total animation duration: 2.5 seconds
- Prevents interaction during animation

src/components/ContentPanel.tsx

@@ -203,10 +203,10 @@ const ContentPanel: React.FC<ContentPanelProps> = ({
     setIsMarkedAsRead(true)
     setShowCheckAnimation(true)
 
-    // Reset animation after it completes
+    // Reset animation after it completes (2.5s for full fancy animation)
     setTimeout(() => {
       setShowCheckAnimation(false)
-    }, 600)
+    }, 2500)
 
     // Fire-and-forget: publish in background without blocking UI
     ;(async () => {