fix: carry all unit data into + Inserat prefill

When clicking + Inserat in UnitStructurePanel, the new listing form
now pre-populates: floor label, fit-out standard, parking, ceiling
height, Mieterausbaubeitrag, Teilbar toggle, min lettable sqm, and
availability date from the unit and its parent property.

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

src/pages/supply/newListingConstants.ts

@@ -49,6 +49,15 @@ export interface LocationState {
     rentPricePerSqm?: number
     unitLabel?: string
     propertyId?: string
+    floor?: string
+    fitOut?: string
+    parking?: number
+    ceilingHeight?: number
+    mieterausbaubeitragPerSqm?: number
+    isFlexible?: boolean
+    minLettableSqm?: number
+    availableFrom?: string
+    softLevels?: Record<string, string>
   }
 }