Introduce series management functionality and repository updates

- Added `series-world.repo.ts` to handle database operations related to series worlds and their elements.
- Implemented `series-sync.repo.ts` for managing synchronization between books and series.
- Expanded `spell.ipc.ts` data models to include `seriesSpellId` for spell synchronization.
- Refactored `insertSpellTag` method in `spelltag.repo.ts` for improved error handling and logic clarity.

electron/database/repositories/chaptercontent.repository.ts

@@ -63,8 +63,7 @@ export default class ChapterContentRepository {
                 LIMIT 1
             `;
             const params: SQLiteValue[] = [userId, bookId];
-            const chapterContents: ChapterContentQueryResult[] = db.all(query, params) as ChapterContentQueryResult[];
-            return chapterContents;
+            return db.all(query, params) as ChapterContentQueryResult[];
         } catch (error: unknown) {
             if (error instanceof Error) {
                 console.error(`DB Error: ${error.message}`);
@@ -127,8 +126,7 @@ export default class ChapterContentRepository {
             const db: Database = System.getDb();
             const query: string = 'SELECT version, content, words_count FROM book_chapter_content WHERE author_id=? AND chapter_id=? AND version=?';
             const params: SQLiteValue[] = [userId, chapterId, version];
-            const companionContents: CompanionContentQueryResult[] = db.all(query, params) as CompanionContentQueryResult[];
-            return companionContents;
+            return db.all(query, params) as CompanionContentQueryResult[];
         } catch (error: unknown) {
             if (error instanceof Error) {
                 console.error(`DB Error: ${error.message}`);