feat(supply): per-unit price/availability editor + mandatory fit-out cost-bearer for shell/edelrohbau

- unit.availableFrom: explicit per-unit availability date
- UnitStructurePanel: inline expandable editor (pencil) for per-unit price + availability via useUpdateUnit
- fitOutByLandlord now boolean|undefined ("not chosen"); toggle has no default for SHELL/BASIC
- NewListing: validate() blocks save until cost-bearer chosen for Rohbau/Edelrohbau
- PropertyDetailView.saveEdit: same guard for existing listings; required asterisk + hint in both forms
- newListingMapper persists explicit tenant(false) choice (was collapsed to undefined)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/components/supply/PropertyDetailOverview.tsx

@@ -39,7 +39,7 @@ export function PropertyDetailOverview({ p, editing, draft, onDraftChange }: Pro
   // Effektive (Draft-überlagerte) hardFacts für den Bearbeiten-Modus
   const hf = draft.hardFacts ?? p.hardFacts ?? {}
   const editFitOut = hf.fitOut ?? ''
-  const editByLandlord = hf.fitOutByLandlord ?? false
+  const editByLandlord = hf.fitOutByLandlord
   const showBuildResponsibility = FIT_OUT_NEEDS_BUILD.has(editFitOut)
   const patchHF = (patch: Partial<NonNullable<Property['hardFacts']>>) =>
     onDraftChange({ ...draft, hardFacts: { ...hf, ...patch } })
@@ -187,17 +187,24 @@ export function PropertyDetailOverview({ p, editing, draft, onDraftChange }: Pro
 
           {showBuildResponsibility && (
             <Box sx={{ mt: 1.5 }}>
-              <Typography variant="caption" color="text.secondary" sx={{ display: 'block', mb: 0.5 }}>Wer baut aus?</Typography>
+              <Typography variant="caption" color="text.secondary" sx={{ display: 'block', mb: 0.5 }}>
+                Wer baut aus? <Box component="span" sx={{ color: '#dc2626' }}>*</Box>
+              </Typography>
               <Box sx={{ display: 'flex', gap: 1.5, alignItems: 'center', flexWrap: 'wrap' }}>
                 <ToggleButtonGroup
                   exclusive size="small"
-                  value={editByLandlord ? 'landlord' : 'tenant'}
+                  value={editByLandlord === undefined ? null : editByLandlord ? 'landlord' : 'tenant'}
                   onChange={(_, v) => { if (v) patchHF({ fitOutByLandlord: v === 'landlord', ...(v === 'landlord' ? { mieterausbaubeitragPerSqm: undefined } : {}) }) }}
                 >
                   <ToggleButton value="landlord" sx={{ textTransform: 'none' }}>Vermieter übernimmt</ToggleButton>
                   <ToggleButton value="tenant" sx={{ textTransform: 'none' }}>Mieter baut aus</ToggleButton>
                 </ToggleButtonGroup>
-                {!editByLandlord && (
+                {editByLandlord === undefined && (
+                  <Typography variant="caption" sx={{ color: '#b45309' }}>
+                    Pflichtangabe bei Rohbau/Edelrohbau
+                  </Typography>
+                )}
+                {editByLandlord === false && (
                   <TextField
                     label="Mieterausbaubeitrag (CHF/m²)"
                     size="small" type="number" sx={{ width: 240 }}