feat(books): surface custom metadata fields in table view

Adds support for displaying custom metadata as columns in the book
table view. The frontend now fetches active fields and dynamically
renders the corresponding cells, backed by book card API updates.

Closes #465

packages/types/src/book.ts

@@ -74,6 +74,7 @@ export type BookCard = {
   hardcoverEditionId?: string | null;
   narrators: string[];
   tags: string[];
+  customMetadata: CustomMetadataBookValue[];
   collapsedSeries?: import("./series-collapse").CollapsedSeriesInfo;
 };
 

packages/types/src/custom-metadata.ts

@@ -17,6 +17,16 @@ export interface CustomMetadataFieldDefinition {
   usageCount: number;
 }
 
+/** Lean summary used for table column building. Omits admin-only attributes (usageCount, timestamps). */
+export interface CustomMetadataFieldSummary {
+  id: number;
+  label: string;
+  type: CustomMetadataFieldType;
+  displayOrder: number;
+  archivedAt: string | null;
+  enabledLibraryIds: number[];
+}
+
 export interface CustomMetadataLibraryEnablement {
   fieldId: number;
   libraryId: number;