fix(spa): cacheControl:false so custom cache headers actually apply

@fastify/static's default Cache-Control management overwrote the
setHeaders values with 'public, max-age=0' (verified on prod after the
v2.4.8 deploy) - the README requires disabling it for custom headers.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/server.ts

@@ -206,6 +206,11 @@ async function start() {
       root: path.join(__dirname, "..", "dist-client"),
       prefix: "/",
       wildcard: false,
+      // The plugin's own Cache-Control management must be OFF or it
+      // overwrites the setHeaders values below with "public, max-age=0"
+      // (README: "To provide a custom Cache-Control header, set this option
+      // to false"). ETags stay on, so no-cache still revalidates cheaply.
+      cacheControl: false,
       // Deploy-skew caching contract (per the Vite deploy guide):
       // - /assets/* names are content-hashed → safe to cache forever
       //   (a changed file always gets a NEW name, so "immutable" is correct).