fix: remove explicit type annotations on Recharts formatter callbacks

TypeScript strict mode in CI rejects explicit parameter types on
Recharts formatter/tickFormatter callbacks. Use inference with
'as number' casts on the value instead. Also fix unsafe cast in
PortfolioComposition and handle possibly-undefined percent.

frontend/src/pages/trading/PerformanceCharts.tsx

@@ -50,7 +50,7 @@ export function PerformanceCharts() {
             <Tooltip
               contentStyle={tooltipStyle}
               labelStyle={{ color: '#9ca3af' }}
-              formatter={(value: number) => [`${value.toFixed(2)}%`, 'Cumulative Return']}
+              formatter={(value) => [`${Number(value).toFixed(2)}%`, 'Cumulative Return']}
             />
             <Line
               type="monotone"
@@ -75,7 +75,7 @@ export function PerformanceCharts() {
             <Tooltip
               contentStyle={tooltipStyle}
               labelStyle={{ color: '#9ca3af' }}
-              formatter={(value: number) => [`${value.toFixed(2)}%`, 'Daily Return']}
+              formatter={(value) => [`${Number(value).toFixed(2)}%`, 'Daily Return']}
             />
             <Bar dataKey="dailyReturn" name="Daily Return">
               {chartData.map((entry, i) => (
@@ -97,7 +97,7 @@ export function PerformanceCharts() {
             <Tooltip
               contentStyle={tooltipStyle}
               labelStyle={{ color: '#9ca3af' }}
-              formatter={(value: number) => [`${value.toFixed(2)}%`, 'Drawdown']}
+              formatter={(value) => [`${Number(value).toFixed(2)}%`, 'Drawdown']}
             />
             <Area
               type="monotone"