feat: add button press feedback

frontend/src/index.css

@@ -95,6 +95,33 @@
     @apply border-border outline-ring/50;
   }
 
+  /* A click should read as a physical state change, not only as a hover ending.
+     Keep the response short and compositor-friendly so repeated actions stay fast. */
+  button:not(:disabled) {
+    transform-origin: center;
+    transition-property: color, background-color, border-color, box-shadow, filter, transform;
+    transition-duration: 140ms;
+    transition-timing-function: cubic-bezier(0.22, 1, 0.36, 1);
+  }
+
+  button:not(:disabled):active {
+    transform: scale(0.97);
+    filter: brightness(0.94);
+    box-shadow: none;
+  }
+
+  @media (prefers-reduced-motion: reduce) {
+    button:not(:disabled) {
+      transition-duration: 0.01ms;
+    }
+
+    button:not(:disabled):active {
+      transform: none;
+      filter: brightness(0.9);
+      box-shadow: none;
+    }
+  }
+
   html {
     @apply font-sans;
   }