fix: tab row counts use investor's scenario, not always Base Case

/api/finanzplan now accepts ?scenarioId and uses it for the per-sheet
row counts (the numbers in brackets on the tab bar). FinanzplanSlide
passes fpBaseScenarioId when fetching the sheet list, so Wandeldarlehen
investors see e.g. Personalkosten (9) instead of (35).

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

pitch-deck/components/slides/FinanzplanSlide.tsx

@@ -100,7 +100,8 @@ export default function FinanzplanSlide({ lang, investorId, preferredScenarioId,
 
   // Load sheet list; populate scenario selector from version data or API fallback
   useEffect(() => {
-    fetch('/api/finanzplan', { cache: 'no-store' })
+    const listParam = fpBaseScenarioId ? `?scenarioId=${fpBaseScenarioId}` : ''
+    fetch(`/api/finanzplan${listParam}`, { cache: 'no-store' })
       .then(r => r.json())
       .then(data => {
         setSheets(data.sheets || [])