feat: Objekt→Einheit architecture — unit-level pre-market, property detail page, click-through from cards

- Domain: PropertyUnit extended with propertyId + schattenmarktRelease per unit
- Domain: FutureAvailabilityResult carries resolved property + unit
- useSchattenmarktSignals: generates unit-level signals (schattenmarkt-{propId}-{unitId})
- useUnifiedResults: resolves backing property + unit on FUTURE_AVAILABILITY fast path
- IUnitProvider + MockupUnitProvider: first-class unit access and mutation
- matchCardAdapter: maps preMarketUnit, preMarketAllUnits, propertyId, unitId to ViewModel
- IntelligenceMatchCard: PRE-MARKET VERIFIED shows unit info strip + "Zur Einheit →" button
- PropertyDetailView: unit-level toggles + date pickers inside PreMarketPanel
- New page: /demand/property/:propertyId with unit table, status chips, inquiry form
- App.tsx: demand route /demand/property/:propertyId registered
- Mock data: prop-001/007/037 units updated with correct lease dates + unit-level schattenmarktRelease

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

src/provider/IUnitProvider.ts

@@ -0,0 +1,7 @@
+import type { PropertyUnit } from '../domain/property'
+
+export interface IUnitProvider {
+  getByPropertyId(propertyId: string): Promise<PropertyUnit[]>
+  getById(unitId: string): Promise<PropertyUnit | null>
+  update(unitId: string, data: Partial<PropertyUnit>): Promise<PropertyUnit>
+}