fix: invalidate properties cache after listing creation

Without this, navigating to Meine Inserate within 5 min of visiting
it previously would show a stale empty list.

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

src/pages/supply/NewListing.tsx

@@ -1,5 +1,6 @@
 import { useState } from 'react'
 import { useLocation, useNavigate } from 'react-router'
+import { useQueryClient } from '@tanstack/react-query'
 import {
   Alert,
   Box,
@@ -76,6 +77,7 @@ interface LocationState {
 
 export default function NewListing() {
   const navigate = useNavigate()
+  const qc = useQueryClient()
   const { state } = useLocation() as { state: LocationState | null }
   const pre = state?.prefill ?? {}
 
@@ -219,6 +221,7 @@ export default function NewListing() {
 
     try {
       await propertyService.create(input)
+      qc.invalidateQueries({ queryKey: ['properties'] })
       setCreated(true)
     } catch {
       setError('Fehler beim Erstellen des Inserats. Bitte erneut versuchen.')