perf(docs): convert godot images to WebP and add cache headers

- Convert godot-iap.png (1.3MB) to WebP (92KB) - 93% reduction
- Convert announcements/godot.png (2.3MB) to WebP (309KB) - 87% reduction
- Add 1-year cache headers for .webp and .png files in vercel.json

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: hyochan

packages/docs/public/announcements/godot.png

@@ -10,7 +10,7 @@ export const LIBRARY_IMAGES = {
   flutter_inapp_purchase:
     'https://hyochan.github.io/flutter_inapp_purchase/img/logo.png',
   'kmp-iap': 'https://hyochan.github.io/kmp-iap/img/logo.png',
-  'godot-iap': '/godot-iap.png',
+  'godot-iap': '/godot-iap.webp',
 } as const;
 
 export type LibraryName = keyof typeof LIBRARY_IMAGES;

packages/docs/public/announcements/godot.webp

@@ -126,7 +126,7 @@ function Announcements() {
             }}
           >
             <img
-              src="/announcements/godot.png"
+              src="/announcements/godot.webp"
               alt="OpenIAP + Godot"
               style={{
                 width: '100%',

packages/docs/public/godot-iap.png

@@ -1,4 +1,24 @@
 {
+  "headers": [
+    {
+      "source": "/(.*).webp",
+      "headers": [
+        {
+          "key": "Cache-Control",
+          "value": "public, max-age=31536000, immutable"
+        }
+      ]
+    },
+    {
+      "source": "/(.*).png",
+      "headers": [
+        {
+          "key": "Cache-Control",
+          "value": "public, max-age=31536000, immutable"
+        }
+      ]
+    }
+  ],
   "rewrites": [
     {
       "source": "/(.*)",