fix(studio-server): revalidate preview assets on every request (#3565)

Project preview assets (images, videos) were served with
Cache-Control: private, max-age=3600, must-revalidate. The 1-hour
max-age let browsers serve stale images from their disk cache without
revalidating, even after the file changed on disk. Hard refresh didn't
recover because it doesn't bypass iframe sub-resource caches.

Switch to `no-cache` so browsers always revalidate against the
existing mtime+size ETag. Unchanged assets still get efficient 304
responses.

Fixes #3564

packages/studio-server/src/routes/preview.ts

@@ -576,7 +576,7 @@ export function registerPreviewRoutes(api: Hono, adapter: PreviewApiAdapter): vo
     const cacheHeaders: Record<string, string> = isText
       ? { "Cache-Control": "no-store" }
       : {
-          "Cache-Control": "private, max-age=3600, must-revalidate",
+          "Cache-Control": "private, no-cache",
           ETag: etag,
         };