Add diagonal view-transition wipe between pages

Hooks SvelteKit's onNavigate into the View Transitions API and styles the
old/new root pseudos with a scaled fade-out and a clip-path diagonal reveal
trimmed by a green drop-shadow accent. Honors prefers-reduced-motion.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

package-lock.json

@@ -13,7 +13,6 @@
       "devDependencies": {
         "@sveltejs/adapter-node": "^5.2.0",
         "@sveltejs/kit": "^2.5.0",
-        "@sveltejs/vite-plugin-svelte": "^3.1.0",
         "svelte": "^4.2.0",
         "vite": "^5.2.0"
       }
@@ -996,6 +995,7 @@
       "integrity": "sha512-Txsm1tJvtiYeLUVRNqxZGKR/mI+CzuIQuc2gn+YCs9rMTowpNZ2Nqt53JdL8KF9bLhAf2ruR/dr9eZCwdTriRA==",
       "dev": true,
       "license": "MIT",
+      "peer": true,
       "dependencies": {
         "@sveltejs/vite-plugin-svelte-inspector": "^2.1.0",
         "debug": "^4.3.4",
@@ -1019,6 +1019,7 @@
       "integrity": "sha512-9QX28IymvBlSCqsCll5t0kQVxipsfhFFL+L2t3nTWfXnddYwxBuAEtTtlaVQpRz9c37BhJjltSeY4AJSC03SSg==",
       "dev": true,
       "license": "MIT",
+      "peer": true,
       "dependencies": {
         "debug": "^4.3.4"
       },
@@ -1227,6 +1228,7 @@
       "integrity": "sha512-RGwwWnwQvkVfavKVt22FGLw+xYSdzARwm0ru6DhTVA3umU5hZc28V3kO4stgYryrTlLpuvgI9GiijltAjNbcqA==",
       "dev": true,
       "license": "MIT",
+      "peer": true,
       "dependencies": {
         "ms": "^2.1.3"
       },
@@ -1585,7 +1587,8 @@
       "resolved": "https://registry.npmjs.org/ms/-/ms-2.1.3.tgz",
       "integrity": "sha512-6FlzubTLZG3J2a/NVCAleEhjzq5oxgHyaCU9yYXvcLsvoVaHJq/s5xXI6/XXP6tz7R9xAOtHnSO/tXtF3WRTlA==",
       "dev": true,
-      "license": "MIT"
+      "license": "MIT",
+      "peer": true
     },
     "node_modules/nanoid": {
       "version": "3.3.12",
@@ -2033,6 +2036,7 @@
       "integrity": "sha512-Gyc7cOS3VJzLlfj7wKS0ZnzDVdv3Pn2IuVeJPk9m2skfhcu5bq3wtIZyQGggr7/Iim5rH5cncyQft/kRLupcnA==",
       "dev": true,
       "license": "ISC",
+      "peer": true,
       "engines": {
         "node": "^12.20 || ^14.13.1 || >= 16"
       },
@@ -2182,6 +2186,7 @@
       "integrity": "sha512-SgHtMLoqaeeGnd2evZ849ZbACbnwQCIwRH57t18FxcXoZop0uQu0uzlIhJBlF/eWVzuce0sHeqPcDo+evVcg8Q==",
       "dev": true,
       "license": "MIT",
+      "peer": true,
       "peerDependencies": {
         "vite": "^3.0.0 || ^4.0.0 || ^5.0.0"
       },

src/routes/+layout.svelte

@@ -1,5 +1,16 @@
 <script>
+  import { onNavigate } from '$app/navigation';
   import Header from '$lib/components/Header.svelte';
+
+  onNavigate((navigation) => {
+    if (!document.startViewTransition) return;
+    return new Promise((resolve) => {
+      document.startViewTransition(async () => {
+        resolve();
+        await navigation.complete;
+      });
+    });
+  });
 </script>
 
 <Header />
@@ -105,4 +116,31 @@
     margin: 0 auto;
     padding: 1.5rem 1.25rem 3rem;
   }
+
+  @keyframes -global-va-fade-out {
+    from { opacity: 1; transform: scale(1);    filter: blur(0); }
+    to   { opacity: 0; transform: scale(0.97); filter: blur(2px); }
+  }
+  @keyframes -global-va-wipe-in {
+    from { clip-path: polygon(0% 0%, 0% 0%, 0% 0%); }
+    to   { clip-path: polygon(0% 0%, 220% 0%, 0% 220%); }
+  }
+  :global(::view-transition-old(root)) {
+    animation: va-fade-out 500ms cubic-bezier(0.4, 0, 1, 1) both;
+    transform-origin: 50% 40%;
+  }
+  :global(::view-transition-new(root)) {
+    animation: va-wipe-in 700ms cubic-bezier(0.76, 0, 0.24, 1) both;
+    filter:
+      drop-shadow(2px 2px 0 #006a4e)
+      drop-shadow(10px 8px 26px rgba(0, 106, 78, 0.22));
+  }
+  @media (prefers-reduced-motion: reduce) {
+    :global(::view-transition-old(root)),
+    :global(::view-transition-new(root)) {
+      animation: none;
+      filter: none;
+      clip-path: none;
+    }
+  }
 </style>