feat(perms): add documents.manage_folders permission

Mirrors files.manage_folders. Gates create / rename / move / delete
of document folders, plus moving documents between folders. Reps with
documents.edit but not manage_folders can rename docs in place but
can't reorganise the tree. Admin + sales_manager get the perm by
default; sales_rep + viewer don't.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/lib/db/schema/users.ts

@@ -39,6 +39,7 @@ export type RolePermissions = {
     send_for_signing: boolean;
     upload_signed: boolean;
     delete: boolean;
+    manage_folders: boolean;
   };
   expenses: {
     view: boolean;