Refactor decryption logic to handle empty fields consistently across services

src-tauri/src/crypto/key_manager.rs

@@ -165,3 +165,7 @@ pub fn get_last_user_id() -> AppResult<Option<String>> {
     let vault = read_vault();
     Ok(vault.last_user_id)
 }
+
+pub fn clear_vault() -> AppResult<()> {
+    write_vault(&SecureVault::default())
+}