Add database schema, encryption utilities, and local database service

- Implement `schema.ts` for SQLite schema creation, indexing, and sync metadata initialization.
- Develop `encryption.ts` with AES-256-GCM encryption utilities for securing database data.
- Add `database.service.ts` to manage CRUD operations with encryption support, user-specific databases, and schema initialization.
- Integrate book, chapter, and character operations with encrypted content handling and sync preparation.

electron/database/mappers/chapter.mapper.ts

@@ -0,0 +1,174 @@
+/**
+ * TypeScript interfaces (copied from lib/models for type safety)
+ */
+
+export interface ChapterContent {
+    version: number;
+    content: string;
+    wordsCount: number;
+}
+
+export interface ChapterProps {
+    chapterId: string;
+    chapterOrder: number;
+    title: string;
+    chapterContent: ChapterContent;
+}
+
+export interface ActChapter {
+    chapterInfoId: string;
+    chapterId: string;
+    title: string;
+    chapterOrder: number;
+    actId: number;
+    incidentId?: string;
+    plotPointId?: string;
+    summary: string;
+    goal: string;
+}
+
+/**
+ * Database row types (snake_case from SQLite)
+ */
+export interface DBChapter {
+    chapter_id: string;
+    book_id: string;
+    author_id: string;
+    title: string;
+    hashed_title?: string;
+    words_count?: number;
+    chapter_order?: number;
+    meta_chapter: string;
+    synced?: number;
+}
+
+export interface DBChapterContent {
+    content_id: string;
+    chapter_id: string;
+    author_id: string;
+    version: number;
+    content: string;
+    words_count: number;
+    meta_chapter_content: string;
+    time_on_it: number;
+    synced?: number;
+}
+
+export interface DBChapterInfo {
+    chapter_info_id: string;
+    chapter_id?: string;
+    act_id?: number;
+    incident_id?: string;
+    plot_point_id?: string;
+    book_id?: string;
+    author_id?: string;
+    summary: string;
+    goal: string;
+    meta_chapter_info: string;
+    synced?: number;
+}
+
+/**
+ * MAPPERS: DB → TypeScript Interfaces
+ */
+
+export function dbToChapter(dbChapter: DBChapter, dbContent?: DBChapterContent): ChapterProps {
+    const chapterContent: ChapterContent = dbContent ? {
+        version: dbContent.version,
+        content: dbContent.content,
+        wordsCount: dbContent.words_count
+    } : {
+        version: 2,
+        content: '',
+        wordsCount: 0
+    };
+
+    return {
+        chapterId: dbChapter.chapter_id,
+        chapterOrder: dbChapter.chapter_order || 0,
+        title: dbChapter.title,
+        chapterContent
+    };
+}
+
+export function dbToChapterContent(dbContent: DBChapterContent): ChapterContent {
+    return {
+        version: dbContent.version,
+        content: dbContent.content,
+        wordsCount: dbContent.words_count
+    };
+}
+
+export function dbToActChapter(dbChapter: DBChapter, dbInfo: DBChapterInfo): ActChapter {
+    return {
+        chapterInfoId: dbInfo.chapter_info_id,
+        chapterId: dbChapter.chapter_id,
+        title: dbChapter.title,
+        chapterOrder: dbChapter.chapter_order || 0,
+        actId: dbInfo.act_id || 0,
+        incidentId: dbInfo.incident_id,
+        plotPointId: dbInfo.plot_point_id,
+        summary: dbInfo.summary,
+        goal: dbInfo.goal
+    };
+}
+
+/**
+ * MAPPERS: TypeScript Interfaces → DB
+ */
+
+export function chapterToDb(chapter: ChapterProps, bookId: string, authorId: string, synced: number = 0): DBChapter {
+    return {
+        chapter_id: chapter.chapterId,
+        book_id: bookId,
+        author_id: authorId,
+        title: chapter.title,
+        hashed_title: '',
+        words_count: chapter.chapterContent.wordsCount,
+        chapter_order: chapter.chapterOrder,
+        meta_chapter: '',
+        synced
+    };
+}
+
+export function chapterContentToDb(
+    content: ChapterContent,
+    contentId: string,
+    chapterId: string,
+    authorId: string,
+    timeOnIt: number = 0,
+    synced: number = 0
+): DBChapterContent {
+    return {
+        content_id: contentId,
+        chapter_id: chapterId,
+        author_id: authorId,
+        version: content.version,
+        content: content.content,
+        words_count: content.wordsCount,
+        meta_chapter_content: '',
+        time_on_it: timeOnIt,
+        synced
+    };
+}
+
+export function actChapterToDbInfo(
+    actChapter: ActChapter,
+    bookId: string,
+    authorId: string,
+    synced: number = 0
+): DBChapterInfo {
+    return {
+        chapter_info_id: actChapter.chapterInfoId,
+        chapter_id: actChapter.chapterId,
+        act_id: actChapter.actId,
+        incident_id: actChapter.incidentId,
+        plot_point_id: actChapter.plotPointId,
+        book_id: bookId,
+        author_id: authorId,
+        summary: actChapter.summary,
+        goal: actChapter.goal,
+        meta_chapter_info: '',
+        synced
+    };
+}