feat(billing): cap each owner's stored file volume

Co-authored-by: Cursor <cursoragent@cursor.com>

apps/api/src/storage/local-file.storage.ts

@@ -32,6 +32,15 @@ export class LocalFileStorage implements OnModuleInit {
     await fs.writeFile(abs, buffer);
   }
 
+  async sizeOf(storageKey: string): Promise<number> {
+    try {
+      const stat = await fs.stat(this.absolutePath(storageKey));
+      return stat.size;
+    } catch {
+      return 0;
+    }
+  }
+
   async remove(storageKey: string): Promise<void> {
     const abs = this.absolutePath(storageKey);
     try {