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/domain/property.ts

@@ -86,6 +86,7 @@ export interface SoftFactors {
 
 export interface PropertyUnit {
   id: string
+  propertyId?: string       // FK to parent Property (set when stored independently)
   floorLevel: number        // 0=EG, 1=1.OG, -1=UG
   unitLabel?: string        // e.g. "Ost", "West", "Einheit A"
   areaSqm: number
@@ -98,6 +99,11 @@ export interface PropertyUnit {
   isFlexible?: boolean      // can be partially leased (Teilfläche)
   minLettableSqm?: number   // minimum area that can be leased standalone
   offeredSqm?: number       // currently offered area (≤ areaSqm); undefined = full unit
+  // Unit-level pre-market release
+  schattenmarktRelease?: {
+    enabled: boolean
+    availableFrom?: string  // ISO date; overrides property-level leaseEndDate for this unit
+  }
 }
 
 // A bundle groups multiple free units for a combined offer