feat: unit-level matching — each floor lettable independently or as bundle

- PropertyUnit: add isFlexible, minLettableSqm, offeredSqm fields
- New UnitBundle + UnitNeedMatch domain types
- unitMatchService: match individual units or bundles against LatentNeeds
  (exact, partial/Teilfläche, bundle match types with area scoring)
- Mock units updated: prop-001/007/012/013 free units flagged as flexible
  with minimum lettable areas
- UnitStructurePanel replaces old Stockwerkstruktur table:
  - Checkboxes on free units (when ≥2 exist) for bundle selection
  - Inline match pills per free unit (top need + score)
  - Expand row to see all matching needs with area details
  - 'Teilfläche möglich' chip for flexible units with min sqm
  - Bundle panel appears when 2+ units selected: shows combined sqm,
    bundle matches, and note about remaining area after contract

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

src/domain/property.ts

@@ -94,6 +94,29 @@ export interface PropertyUnit {
   currentTenant?: string
   leaseTerm?: string
   leaseEndDate?: string
+  // Flexible letting
+  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
+}
+
+// A bundle groups multiple free units for a combined offer
+export interface UnitBundle {
+  unitIds: string[]
+  combinedSqm: number
+  label: string             // e.g. "1.OG + 2.OG"
+}
+
+// Result of unit-level need matching
+export interface UnitNeedMatch {
+  needId: string
+  tenantName: string
+  tenantCompany?: string
+  requiredSqmMin: number
+  requiredSqmMax: number
+  matchScore: number
+  matchType: 'exact' | 'partial' | 'bundle'  // how the unit satisfies the need
+  suggestedSqm?: number     // for partial: how much of the unit to offer
 }
 
 // ── Property ──────────────────────────────────────────────────────────────────