fix: remove broken capital controls, reset now queries broker for real balance

- Removed PUT /api/trading/capital (set capital) — only touched in-memory state
- Removed POST /api/trading/capital/adjust (add/withdraw) — same problem
- Reset endpoint now: liquidates Alpaca positions, cancels orders, clears DB,
  then queries Alpaca for real portfolio_value to set engine capital
- Frontend: replaced CapitalCard with simple ResetCard (one button)
- Removed useSetTradingCapital and useAdjustCapital hooks

frontend/src/api/hooks.ts

@@ -426,15 +426,6 @@ export function useSetTradingMode() {
   });
 }
 
-export function useSetTradingCapital() {
-  const qc = useQueryClient();
-  return useMutation({
-    mutationFn: (initial_capital: number) =>
-      apiPut<{ initial_capital: number; active_pool: number; reserve_pool: number }>('trading', '/api/trading/capital', { initial_capital }),
-    onSuccess: () => qc.invalidateQueries({ queryKey: ['trading-config'] }),
-  });
-}
-
 export function usePendingApprovals() {
   return useGet<Approval[]>(['pending-approvals'], 'query', '/api/admin/trading/approvals');
 }