Add models for guidelines, incidents, plot points, issues, acts, and world data

- Introduced new models: `GuideLine`, `Incident`, `PlotPoint`, `Issue`, `Act`, and `World` for managing book-related entities.
- Integrated encryption/decryption for sensitive properties in all models using user-specific keys.
- Added methods for CRUD operations and synchronization workflows with error handling and multilingual support.
- Improved maintainability with JSDoc comments and streamlined queries.

electron/database/models/EpubStyle.ts

@@ -1,4 +1,16 @@
-export const mainStyle = `h1 {
+/**
+ * Default CSS styles for EPUB export formatting.
+ *
+ * These styles are applied to the generated EPUB content to ensure
+ * consistent typography and layout across different e-readers.
+ *
+ * @remarks
+ * - h1 elements: 24px bold font with 24px text indentation
+ * - p elements: 30px text indentation, 0.7em vertical margins, justified text
+ *
+ * All styles use !important to override e-reader default styles.
+ */
+export const mainStyle: string = `h1 {
   font-size: 24px !important;
   font-weight: bold !important;
   text-indent: 24px !important;