feat: add prerendered error pages with Rust integration

- Prerender 20+ HTTP error codes (4xx/5xx) at build time
- Embed error pages in binary and serve via Axum
- Intercept error responses for HTML requests
- Add transient flag for retry-worthy errors (502/503/504)

web/svelte.config.js

@@ -8,16 +8,19 @@ const config = {
   kit: {
     adapter: adapter({
       out: "build",
-      precompress: {
-        brotli: true,
-        gzip: true,
-        files: ["html", "js", "json", "css", "svg", "xml", "wasm"],
-      },
+      precompress: true,
       serveAssets: false,
     }),
     alias: {
       $components: "src/lib/components",
     },
+    prerender: {
+      handleHttpError: ({ path, referrer, message }) => {
+        console.log(
+          `Prerender error for ${path} (from ${referrer}): ${message}`,
+        );
+      },
+    },
   },
 };