Migrate from window.electron to tauri IPC functions across components

- 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.

src-tauri/src/domains/cover/mod.rs

@@ -0,0 +1 @@
+pub mod service;

src-tauri/src/domains/cover/service.rs

@@ -0,0 +1,53 @@
+use std::fs;
+use std::path::Path;
+
+use base64::{engine::general_purpose::STANDARD as BASE64, Engine};
+use rusqlite::Connection;
+
+use crate::crypto::encryption::decrypt_data_with_user_key;
+use crate::crypto::key_manager::get_user_encryption_key;
+use crate::domains::book::repo;
+use crate::error::AppResult;
+use crate::helpers::timestamp_in_seconds;
+use crate::shared::types::Lang;
+
+/// Retrieves and decrypts the cover picture for a specific book.
+/// Returns the decrypted cover image data, or an empty string if not found.
+pub fn get_cover_picture(conn: &Connection, user_id: &str, book_id: &str, lang: Lang) -> AppResult<String> {
+    let cover_query: repo::BookCoverQuery = repo::fetch_book_cover(conn, user_id, book_id, lang)?;
+    if !cover_query.cover_image.is_empty() {
+        let user_encryption_key: String = get_user_encryption_key(user_id)?;
+        decrypt_data_with_user_key(&cover_query.cover_image, &user_encryption_key)
+    } else {
+        Ok(String::new())
+    }
+}
+
+/// Deletes the cover picture association for a specific book.
+/// Clears the cover image reference in the database.
+/// Returns true if the cover was successfully deleted, false otherwise.
+pub fn delete_cover_picture(conn: &Connection, user_id: &str, book_id: &str, lang: Lang) -> AppResult<bool> {
+    let _existing_cover_name: String = get_cover_picture(conn, user_id, book_id, lang)?;
+    let last_update: i64 = timestamp_in_seconds();
+    repo::update_book_cover(conn, book_id, "", user_id, last_update, lang)
+}
+
+/// Retrieves and decrypts a picture file, returning it as a base64-encoded string.
+/// Returns the base64-encoded image data, or an empty string if the image cannot be read.
+pub fn get_picture(_user_id: &str, user_key: &str, image: &str, _lang: Lang) -> String {
+    if image.is_empty() {
+        return String::new();
+    }
+    match try_get_picture(user_key, image) {
+        Ok(base64_data) => base64_data,
+        Err(_) => String::new(),
+    }
+}
+
+fn try_get_picture(user_key: &str, image: &str) -> AppResult<String> {
+    let decrypted_file_name: String = decrypt_data_with_user_key(image, user_key)?;
+    let user_directory: &Path = Path::new(&decrypted_file_name);
+    let file_data: Vec<u8> = fs::read(user_directory)
+        .map_err(|error| crate::error::AppError::Internal(error.to_string()))?;
+    Ok(BASE64.encode(&file_data))
+}