fix(quota): stop /me/quota leaking raw disk to guests

The per-user quota widget was shown to everyone and the /me/quota payload returned
free_disk_bytes (raw server free space) and active_uploaders to any authenticated
guest. Gate the widget to staff (host/admin) on the upload and account pages, and zero
the server-wide telemetry fields for non-staff in the handler. Guests still get their
own used/limit so enforcement stays transparent.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/src/handlers/me.rs

@@ -14,7 +14,7 @@ use serde::Serialize;
 use crate::auth::middleware::AuthUser;
 use crate::error::AppError;
 use crate::handlers::upload::compute_storage_quota;
-use crate::models::user::User;
+use crate::models::user::{User, UserRole};
 use crate::services::config;
 use crate::state::AppState;
 
@@ -37,12 +37,26 @@ pub async fn get_quota(
 
     let estimate = compute_storage_quota(&state).await;
 
+    // Raw server telemetry (free disk, concurrent uploader count) is staff-only — it
+    // must never reach a guest, even though the guest upload UI no longer renders it.
+    // A guest still gets their own `used`/`limit` so enforcement stays transparent to
+    // the code paths that consume it; only the server-wide fields are zeroed.
+    let is_staff = matches!(auth.role, UserRole::Host | UserRole::Admin);
+
     Ok(Json(QuotaDto {
         enabled: estimate.limit_bytes.is_some(),
         used_bytes: user.total_upload_bytes,
         limit_bytes: estimate.limit_bytes,
-        active_uploaders: estimate.active_uploaders,
-        free_disk_bytes: estimate.free_disk_bytes,
+        active_uploaders: if is_staff {
+            estimate.active_uploaders
+        } else {
+            0
+        },
+        free_disk_bytes: if is_staff {
+            estimate.free_disk_bytes
+        } else {
+            0
+        },
     }))
 }