fix: P0 stabilisation — score modifiers, logout cache clear, provider isolation, mutation error feedback

- scoreCalculator: apply dataQuality/confidence modifiers to finalScore (were computed but hardcoded to 0)
- authService: call queryClient.clear() on logout to prevent cross-session data leakage
- queryClient: extract to src/lib/queryClient.ts singleton so services can access it without circular imports
- matchSyncService: new service layer owns match-generation logic; MockupNeedProvider no longer imports other providers directly
- hooks (11 files): add onError + German toast feedback to every useMutation

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

src/hooks/useOffers.ts

@@ -1,6 +1,7 @@
 import { useMutation } from '@tanstack/react-query'
 import { offerService } from '../services/offerService'
 import type { AssetType } from '../domain/enums'
+import { useToastStore } from '../stores/toastStore'
 
 export function useCreateOfferDraft() {
   return useMutation({
@@ -20,6 +21,9 @@ export function useCreateOfferDraft() {
         input.assetType,
         input.sizeRange,
       ),
+    onError: () => {
+      useToastStore.getState().showToast('Angebot konnte nicht erstellt werden.', 'error')
+    },
   })
 }
 
@@ -27,23 +31,35 @@ export function useUpdateOfferField() {
   return useMutation({
     mutationFn: (input: { offerDraftId: string; fieldId: string; value: string }) =>
       offerService.updateOfferField(input.offerDraftId, input.fieldId, input.value),
+    onError: () => {
+      useToastStore.getState().showToast('Feld konnte nicht gespeichert werden.', 'error')
+    },
   })
 }
 
 export function useMarkOfferChecked() {
   return useMutation({
     mutationFn: (offerDraftId: string) => offerService.markOfferChecked(offerDraftId),
+    onError: () => {
+      useToastStore.getState().showToast('Prüfung konnte nicht gespeichert werden.', 'error')
+    },
   })
 }
 
 export function useGeneratePdfPreview() {
   return useMutation({
     mutationFn: (offerDraftId: string) => offerService.generatePdfPreview(offerDraftId),
+    onError: () => {
+      useToastStore.getState().showToast('PDF-Vorschau konnte nicht generiert werden.', 'error')
+    },
   })
 }
 
 export function useSendOffer() {
   return useMutation({
     mutationFn: (offerDraftId: string) => offerService.sendOffer(offerDraftId),
+    onError: () => {
+      useToastStore.getState().showToast('Angebot konnte nicht gesendet werden. Bitte versuchen Sie es erneut.', 'error')
+    },
   })
 }