Fix TS errors: vite/client types + recharts Tooltip formatter signature

frontend/src/pages/Rolling12Months.tsx

@@ -136,7 +136,7 @@ export default function Rolling12Months() {
               <BarChart data={chartData} margin={{ top: 4, right: 16, left: 16, bottom: 0 }}>
                 <XAxis dataKey="label" tick={{ fontSize: 10 }} />
                 <YAxis tickFormatter={v => `£${Math.round(v / 1000)}k`} tick={{ fontSize: 11 }} width={55} />
-                <Tooltip formatter={(v: number) => fmtMoney(v)} />
+                <Tooltip formatter={(v: unknown) => fmtMoney(Number(v))} />
                 <Legend />
                 {deptCols.map(dep => (
                   <Bar key={dep.id} dataKey={dep.name} stackId="a" fill={dep.color} />