style(motion): add strict animations and fix layout properties

- Change ReadingProgress and RouteTable to use transform (scaleX/scaleY) instead of width/height
- Convert existing easing functions to 200ms cubic-bezier(.2,0,0,1)
- Document animation purpose with CSS comments
- Add guide panel swap, review desk detail swap, and tally pop animations
- Implement prefers-reduced-motion for all new states

src/components/islands/GuideSelector.astro

@@ -99,7 +99,11 @@ const { rootSelector, data } = Astro.props;
 
     function replace(target, markup) {
       const panel = root.querySelector(target);
-      if (panel) panel.innerHTML = markup;
+      if (!panel) return;
+      panel.innerHTML = markup;
+      panel.classList.remove('is-swapping');
+      void panel.offsetWidth;
+      panel.classList.add('is-swapping');
     }
 
     // Names deliberately match legacy functions until task 19 updates its checks.
@@ -291,4 +295,24 @@ const { rootSelector, data } = Astro.props;
     outline: 3px solid var(--gold);
     outline-offset: -3px;
   }
+
+  :global(.is-swapping > *) {
+    /* purpose: tab panel change in the guide (state change) */
+    animation: guide-swap 200ms cubic-bezier(0.2, 0, 0, 1) both;
+  }
+  @keyframes guide-swap {
+    from {
+      opacity: 0.15;
+      transform: translateY(5px);
+    }
+    to {
+      opacity: 1;
+      transform: translateY(0);
+    }
+  }
+  @media (prefers-reduced-motion: reduce) {
+    :global(.is-swapping > *) {
+      animation: none;
+    }
+  }
 </style>