- Introduced `DatabaseManager` for handling SQLite connections per user with WAL and foreign key support.
- Implemented `initialize_schema` to set up comprehensive database schema covering AI, books, characters, locations, series, and sync tracking.
- Added migration helpers for schema versioning and column updates.
- Structured database module into `connection.rs` and `schema.rs` for clearer organization.
- Replaced `window.electron.invoke` calls with equivalent `tauri` function calls for all IPC interactions.
- Removed `electron.d.ts` TypeScript definitions as they are no longer needed.
- Updated related logic for offline/online state synchronization.
- Added `types.rs` and `shared/mod.rs` modules to support Tauri IPC integration with Rust enums and shared logic.
- Refactored IPC request queues to use updated handler names for consistency with Tauri.
