feat: Marktchancen — Netzwerk-Hinweise tab (human-sourced market intel)

- MarktHinweis domain type: SUCHE/VERFUEGBARKEIT direction, INTERN/PLATTFORM
  visibility, anonymization flag, source tracking
- Full data layer: IMarktHinweisProvider, MockupMarktHinweisProvider, service, hooks
- 7 seed entries: mix of intern/shared, demand/supply, own/partner Verwaltungen
- Marktchancen gets two-tab layout: Digitale Signale (crawler) + Netzwerk (human)
- HinweisListItem: direction icon, visibility badge (Intern/Geteilt/partner name)
- HinweisDetail: note card, portfolio match (SUCHE) or availability info (VERFUEGBARKEIT)
- HinweisErfassenDialog: direction toggle, asset type, location, area range,
  company + anonymize switch, source, note, card-based visibility picker
- HinweisPropertyCard: same Anschreiben composer pattern as crawler side

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

src/hooks/useMarktHinweise.ts

@@ -0,0 +1,21 @@
+import { useQuery, useMutation, useQueryClient } from '@tanstack/react-query'
+import { marktHinweisService } from '../services/marktHinweisService'
+import type { CreateMarktHinweisInput } from '../domain/marktHinweis'
+
+export function useMarktHinweise() {
+  return useQuery({
+    queryKey: ['marktHinweise'],
+    queryFn: () => marktHinweisService.getAll(),
+    staleTime: 60_000,
+  })
+}
+
+export function useCreateMarktHinweis() {
+  const queryClient = useQueryClient()
+  return useMutation({
+    mutationFn: (data: CreateMarktHinweisInput) => marktHinweisService.create(data),
+    onSuccess: () => {
+      queryClient.invalidateQueries({ queryKey: ['marktHinweise'] })
+    },
+  })
+}