fix: raise upload size cap from 500 MB to 5 GB

The 500 MB cap was arbitrary. Self-hosted admins should decide based
on their own disk space. Global multipart ceiling raised to 5 GB,
validation cap to 5120 MB.

packages/server/src/index.ts

@@ -61,7 +61,7 @@ async function main(): Promise<void> {
 
   await app.register(multipart, {
     limits: {
-      fileSize: 500 * 1024 * 1024,  // 500MB hard ceiling — actual limit enforced per-request
+      fileSize: 5 * 1024 * 1024 * 1024,  // 5GB hard ceiling — actual limit enforced per-request from DB
     },
   });