docs: fix misleading middleware example path in routing docs (#4354)

Author: rafaumeu

docs/1.docs/5.routing.md

@@ -271,13 +271,16 @@ export default defineConfig({
   handlers: [
     {
       route: "/api/**",
-      handler: "./server/middleware/api-auth.ts",
+      handler: "./server/utils/api-auth.ts",
       middleware: true,
     },
   ],
 });
 ```
 
+> [!WARNING]
+> When using `handlers` for route-scoped middleware, place handler files outside the `server/middleware/` directory. Files in `server/middleware/` run globally for all requests regardless of the `route` pattern.
+
 Each handler entry supports the following options:
 
 | Option | Type | Description |
@@ -408,7 +411,7 @@ export default defineConfig({
   handlers: [
     {
       route: "/api/**",
-      handler: "./server/middleware/api-auth.ts",
+      handler: "./server/utils/api-auth.ts",
       middleware: true,
     },
   ],