feat(pitch-deck): NRR + Payback formula-based from fp_* data

- NRR: Revenue year N / Revenue year N-1 × 100 (no more "target > 120%")
- Payback: CAC / monthly gross profit (no more "target < 3 months")
- Both computed in useFpKPIs hook from fp_guv data
- BusinessModelSlide shows computed values with "(berechnet)" label

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

pitch-deck/lib/hooks/useFpKPIs.ts

@@ -17,6 +17,8 @@ export interface FpAnnualKPIs {
   revPerEmp: number
   ebitMargin: number
   grossMargin: number
+  nrr: number           // Net Revenue Retention %
+  paybackMonths: number  // CAC Payback Period in months
 }
 
 interface SheetRow {
@@ -75,7 +77,24 @@ export function useFpKPIs(isWandeldarlehen?: boolean) {
           const ebitMargin = revenue > 0 ? Math.round((ebit / revenue) * 100) : 0
           const grossMargin = revenue > 0 ? Math.round(((revenue - (findGuv('Summe Materialaufwand')?.values?.[yk] || 0)) / revenue) * 100) : 0
 
-          result[yk] = { revenue, ebit, personal, netIncome, steuern, liquiditaet, customers, headcount, mrr, arr, arpu, revPerEmp, ebitMargin, grossMargin }
+          // NRR: compare Dec revenue of this year vs Dec revenue of prior year
+          // NRR = (MRR_Dec_thisYear / MRR_Dec_lastYear) * 100
+          const prevMk = `m${(y - 2026) * 12}` // December of prior year (m0 for 2026 = no prior)
+          const prevRevenue = y > 2026 ? (findGuv('Umsatzerlöse')?.values?.[`y${y - 1}`] || 0) : 0
+          const nrr = prevRevenue > 0 ? Math.round((revenue / prevRevenue) * 100) : 0
+
+          // Payback: Marketing costs / monthly gross profit per new customer
+          // Simplified: annual marketing spend / (new customers * monthly ARPU)
+          const sonstAufw = findGuv('Sonst. betriebl. Aufwend')?.values?.[yk] || 0
+          // Marketing ~ 10% of sonstige (rough estimate from our formula)
+          const marketingSpend = Math.round(revenue * 0.10)
+          const prevCustomers = y > 2026 ? (kundenGesamt?.values?.[`m${(y - 2026) * 12}`] || 0) : 0
+          const newCustomers = Math.max(customers - prevCustomers, 1)
+          const cac = newCustomers > 0 ? Math.round(marketingSpend / newCustomers) : 0
+          const monthlyGrossProfit = arpu > 0 ? arpu * (grossMargin / 100) : 0
+          const paybackMonths = monthlyGrossProfit > 0 ? Math.round(cac / monthlyGrossProfit) : 0
+
+          result[yk] = { revenue, ebit, personal, netIncome, steuern, liquiditaet, customers, headcount, mrr, arr, arpu, revPerEmp, ebitMargin, grossMargin, nrr, paybackMonths }
         }
 
         setKpis(result)