refactor: unit-centric lease view — Einheiten & Mietverträge

Replace building-level Miet- & Mieterinformationen section with
unit-level lease display. Each unit row now shows tenant name and
lease end date directly; expand reveals full contract details
(Mietbeginn, Mietende, Laufzeit, Breakout, source system, doc link).

Floor grouping groups consecutive same-floor units under one label.
Domain model extended with Lease and Tenant types; deprecated
property-level tenant fields preserved via @deprecated for compat.

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

src/domain/unit.ts

@@ -1,22 +1,30 @@
 // ── Rentable Unit — primary entity for demand-side matching ──────────────────
 //
-// A Property is the building/address container.
-// A PropertyUnit is what is actually rented: a specific floor, wing, or section.
-// Floor level is business-critical: retail needs EG for walk-in traffic,
-// offices can occupy upper floors, logistics needs ground-level loading access.
+// A Property is the building/address container (Liegenschaft).
+// A PropertyUnit is what is actually rented: a specific floor, wing, or section (Mietobjekt).
+// Floor level is an attribute of the unit — not a separate entity (matches Garaio REM / SAP RE-FX).
+// Tenant and contract data live on Lease, not directly on the unit.
+
+import type { Lease } from './lease'
+import type { AvailabilityStatus } from './enums'
+import { AvailabilityStatus as AS } from './enums'
 
 export interface PropertyUnit {
   id: string
-  propertyId?: string       // FK to parent Property
+  propertyId?: string       // FK to parent Property (Liegenschaft)
   floorLevel: number        // 0=EG, 1=1.OG, -1=UG1
   unitLabel?: string        // e.g. "Nord", "West", "Einheit A"
   areaSqm: number
   available: boolean
   rentPricePerSqm?: number  // annual CHF/m²; falls back to property.rentPricePerSqm
+  leases?: Lease[]          // Mietverträge — current, historical, future
+  /** @deprecated Use leases[].tenant.companyName */
   currentTenant?: string
-  leaseTerm?: string
+  /** @deprecated Use leases[].endDate */
   leaseEndDate?: string
-  floorPlanUrl?: string        // optional floor plan image
+  /** @deprecated Use leases[0].contractDurationYears */
+  leaseTerm?: string
+  floorPlanUrl?: string
   // Flexible letting (Teilfläche)
   isFlexible?: boolean
   minLettableSqm?: number
@@ -28,6 +36,23 @@ export interface PropertyUnit {
   }
 }
 
+// Derives availability from the unit's lease list.
+// Use this instead of reading property.availabilityStatus directly.
+export function getUnitAvailability(unit: PropertyUnit): {
+  status: AvailabilityStatus
+  availableFrom?: string
+  activeLease?: Lease
+} {
+  const active = unit.leases?.find(l => l.status === 'ACTIVE')
+  if (!active) return { status: AS.AVAILABLE_NOW }
+  const now = new Date()
+  const monthsToEnd = (new Date(active.endDate).getTime() - now.getTime()) / (1000 * 60 * 60 * 24 * 30)
+  if (monthsToEnd <= 12) {
+    return { status: AS.AVAILABLE_SOON, availableFrom: active.endDate, activeLease: active }
+  }
+  return { status: AS.OCCUPIED, activeLease: active }
+}
+
 // A bundle groups multiple free units into a combined offer
 export interface UnitBundle {
   unitIds: string[]