feat(i18n): add alias type labels and section strings for de/en/es

Adds 16 new keys per language: alias type labels (BIRTH, WIDOWED,
DIVORCED, OTHER), section heading, empty state, add form labels,
delete confirmation, and ALIAS_NOT_FOUND error code.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/lib/errors.ts

@@ -6,6 +6,7 @@ import * as m from '$lib/paraglide/messages.js';
  */
 export type ErrorCode =
 	| 'PERSON_NOT_FOUND'
+	| 'ALIAS_NOT_FOUND'
 	| 'DOCUMENT_NOT_FOUND'
 	| 'DOCUMENT_NO_FILE'
 	| 'FILE_NOT_FOUND'
@@ -52,6 +53,8 @@ export function getErrorMessage(code: ErrorCode | string | undefined): string {
 	switch (code) {
 		case 'PERSON_NOT_FOUND':
 			return m.error_person_not_found();
+		case 'ALIAS_NOT_FOUND':
+			return m.error_alias_not_found();
 		case 'DOCUMENT_NOT_FOUND':
 			return m.error_document_not_found();
 		case 'DOCUMENT_NO_FILE':