feat: add duplicate account import prevention

- Add duplicate check in ImportAccountView before account import
- Add duplicate check in ImportDerivedAccountView for derived accounts
- Add safety check in saveNewIdentity function to prevent duplicate saves
- Implement user-friendly warning messages for duplicate attempts
- Add comprehensive error handling to catch duplicate errors from saveNewIdentity
- Create Playwright tests to verify duplicate prevention functionality
- Add documentation for duplicate prevention implementation

The system now prevents users from importing the same account multiple times
by checking for existing DIDs both before import (pre-check) and during
save (post-check). Users receive clear warning messages instead of
technical errors when attempting to import duplicate accounts.

Files modified:
- src/views/ImportAccountView.vue: Add duplicate check and error handling
- src/views/ImportDerivedAccountView.vue: Add duplicate check for derived accounts
- src/libs/util.ts: Add duplicate prevention in saveNewIdentity
- test-playwright/duplicate-import-test.spec.ts: Add comprehensive tests
- doc/duplicate-account-import-implementation.md: Add implementation docs

Resolves: Prevent duplicate account imports in IdentitySwitcherView

src/views/ImportDerivedAccountView.vue

@@ -171,6 +171,16 @@ export default class ImportAccountView extends Vue {
     const newId = newIdentifier(address, publicHex, privateHex, newDerivPath);
 
     try {
+      // Check for duplicate account before creating
+      const isDuplicate = await this.checkForDuplicateAccount(newId.did);
+      if (isDuplicate) {
+        this.notify.warning(
+          "This derived account already exists. Please try a different derivation path.",
+          TIMEOUTS.LONG,
+        );
+        return;
+      }
+
       await saveNewIdentity(newId, mne, newDerivPath);
 
       // record that as the active DID
@@ -192,5 +202,27 @@ export default class ImportAccountView extends Vue {
       this.notify.error(NOTIFY_ACCOUNT_DERIVATION_ERROR.message, TIMEOUTS.LONG);
     }
   }
+
+  /**
+   * Checks if the account to be created already exists
+   *
+   * @param did - The DID to check for duplicates
+   * @returns Promise<boolean> - True if account already exists, false otherwise
+   */
+  private async checkForDuplicateAccount(did: string): Promise<boolean> {
+    try {
+      // Check if an account with this DID already exists
+      const existingAccount = await this.$query(
+        "SELECT did FROM accounts WHERE did = ?",
+        [did],
+      );
+
+      return existingAccount?.values?.length > 0;
+    } catch (error) {
+      // If we can't check for duplicates, let the save process handle the error
+      this.$logError("Error checking for duplicate account: " + error);
+      return false;
+    }
+  }
 }
 </script>