fix(smart-scope): handle invalid filters gracefully in count calculation

Validate smart scope filter rules before constructing query clauses during count computation. Catch validation errors for broken rules so invalid filters return null for bookCount rather than triggering an internal server error when fetching all smart scopes.

Closes #787

packages/types/src/smart-scope.ts

@@ -10,7 +10,7 @@ export interface SmartScope {
   isPublic: boolean;
   syncToKobo: boolean;
   displayOrder: number;
-  bookCount?: number;
+  bookCount?: number | null;
   createdAt: string;
   updatedAt: string;
 }