feat(error): add JOURNEY_AT_CAPACITY error code with i18n (de/en/es)

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

backend/src/main/java/org/raddatz/familienarchiv/exception/ErrorCode.java

@@ -126,6 +126,8 @@ public enum ErrorCode {
     JOURNEY_ITEM_NOT_FOUND,
     /** A position uniqueness conflict occurred on the journey_items table — concurrent append or reorder. 409 */
     JOURNEY_ITEM_POSITION_CONFLICT,
+    /** The journey already has the maximum allowed number of items (100). 400 */
+    JOURNEY_AT_CAPACITY,
 
     // --- Tags ---
     /** A tag with the given ID does not exist. 404 */

frontend/messages/de.json

@@ -1025,6 +1025,7 @@
 	"error_geschichte_not_found": "Die Geschichte wurde nicht gefunden.",
 	"error_journey_item_not_found": "Der Reise-Eintrag wurde nicht gefunden.",
 	"error_journey_item_position_conflict": "Die Reihenfolge wurde gerade von jemand anderem geändert – bitte laden Sie die Seite neu.",
+	"error_journey_at_capacity": "Die Lesereise hat bereits die maximale Anzahl von Einträgen (100) erreicht.",
 	"geschichten_index_title": "Geschichten",
 	"geschichten_new_button": "Neue Geschichte",
 	"geschichten_filter_all_pill": "Alle",

frontend/messages/en.json

@@ -1025,6 +1025,7 @@
 	"error_geschichte_not_found": "The story was not found.",
 	"error_journey_item_not_found": "The journey item was not found.",
 	"error_journey_item_position_conflict": "The order was just changed by someone else — please reload the page.",
+	"error_journey_at_capacity": "The reading journey has already reached the maximum of 100 items.",
 	"geschichten_index_title": "Stories",
 	"geschichten_new_button": "New story",
 	"geschichten_filter_all_pill": "All",

frontend/messages/es.json

@@ -1025,6 +1025,7 @@
 	"error_geschichte_not_found": "No se encontró la historia.",
 	"error_journey_item_not_found": "No se encontró el elemento del viaje.",
 	"error_journey_item_position_conflict": "El orden fue cambiado por otra persona — por favor recargue la página.",
+	"error_journey_at_capacity": "El viaje de lectura ya ha alcanzado el máximo de 100 entradas.",
 	"geschichten_index_title": "Historias",
 	"geschichten_new_button": "Nueva historia",
 	"geschichten_filter_all_pill": "Todas",

frontend/src/lib/shared/errors.ts

@@ -48,6 +48,7 @@ export type ErrorCode =
 	| 'GESCHICHTE_NOT_FOUND'
 	| 'JOURNEY_ITEM_NOT_FOUND'
 	| 'JOURNEY_ITEM_POSITION_CONFLICT'
+	| 'JOURNEY_AT_CAPACITY'
 	| 'INVALID_CREDENTIALS'
 	| 'SESSION_EXPIRED'
 	| 'MISSING_CREDENTIALS'
@@ -170,6 +171,8 @@ export function getErrorMessage(code: ErrorCode | string | undefined): string {
 			return m.error_journey_item_not_found();
 		case 'JOURNEY_ITEM_POSITION_CONFLICT':
 			return m.error_journey_item_position_conflict();
+		case 'JOURNEY_AT_CAPACITY':
+			return m.error_journey_at_capacity();
 		case 'INVALID_CREDENTIALS':
 			return m.error_invalid_credentials();
 		case 'SESSION_EXPIRED':