fix(buchhaltung): format transaction IDs as YYYY/NR and deduplicate dashboard widgets

frontend/src/pages/Buchhaltung.tsx

@@ -1219,7 +1219,7 @@ function TransaktionenTab({ haushaltsjahre, selectedJahrId, onJahrChange }: {
               )}
               {subTabTransaktionen.map((t: Transaktion) => (
                 <TableRow key={t.id} hover>
-                  <TableCell>{t.laufende_nummer ?? `E${t.id}`}</TableCell>
+                  <TableCell>{t.laufende_nummer != null ? `${t.haushaltsjahr_jahr}/${t.laufende_nummer}` : `E${t.id}`}</TableCell>
                   <TableCell>{fmtDate(t.datum)}</TableCell>
                   <TableCell>
                     <Chip

frontend/src/pages/Dashboard.tsx

@@ -198,7 +198,7 @@ function Dashboard() {
             const allKeys = DEFAULT_ORDER[group];
             const ordered = saved.filter((k: string) => allKeys.includes(k) && !customGroupKeys.has(k));
             const remaining = allKeys.filter((k) => !allSavedKeys.has(k));
-            merged[group] = [...ordered, ...remaining];
+            merged[group] = [...new Set([...ordered, ...remaining])];
           }
         }
         // Include custom groups from preferences
@@ -206,7 +206,7 @@ function Dashboard() {
           for (const cg of preferences.customGroups as { name: string; title: string }[]) {
             if (!merged[cg.name]) merged[cg.name] = [];
             if (preferences.widgetOrder[cg.name]) {
-              merged[cg.name] = preferences.widgetOrder[cg.name] as string[];
+              merged[cg.name] = [...new Set(preferences.widgetOrder[cg.name] as string[])];
             }
           }
         }

frontend/src/types/buchhaltung.types.ts

@@ -133,6 +133,7 @@ export interface Transaktion {
   konto_id: number | null;
   bankkonto_id: number | null;
   laufende_nummer: number | null;
+  haushaltsjahr_jahr?: number;
   typ: TransaktionTyp;
   betrag: number;
   datum: string;