refactor: move duplicate account import warnings to notification constants

- Add NOTIFY_DUPLICATE_ACCOUNT_IMPORT constant for import warnings
- Add NOTIFY_DUPLICATE_DERIVED_ACCOUNT constant for derived account warnings
- Update ImportAccountView.vue to use notification constants
- Update ImportDerivedAccountView.vue to use notification constants
- Update test file to use notification constants for assertions

Centralizes notification messages for better maintainability and consistency
with the existing notification system.

Files modified:
- src/constants/notifications.ts: Add new notification constants
- src/views/ImportAccountView.vue: Replace hardcoded messages with constants
- src/views/ImportDerivedAccountView.vue: Replace hardcoded messages with constants
- test-playwright/duplicate-import-test.spec.ts: Update test assertions

src/constants/notifications.ts

@@ -1689,3 +1689,19 @@ export const NOTIFY_CONTACTS_ADDED_CONFIRM = {
   title: "They're Added To Your List",
   message: "Would you like to go to the main page now?",
 };
+
+// ImportAccountView.vue specific constants
+// Used in: ImportAccountView.vue (onImportClick method - duplicate account warning)
+export const NOTIFY_DUPLICATE_ACCOUNT_IMPORT = {
+  title: "Account Already Imported",
+  message:
+    "This account has already been imported. Please use a different seed phrase or check your existing accounts.",
+};
+
+// ImportDerivedAccountView.vue specific constants
+// Used in: ImportDerivedAccountView.vue (incrementDerivation method - duplicate derived account warning)
+export const NOTIFY_DUPLICATE_DERIVED_ACCOUNT = {
+  title: "Derived Account Already Exists",
+  message:
+    "This derived account already exists. Please try a different derivation path.",
+};