fix(frontend): correct events amount sign for actual-negative rows

Spec review of Task 9 caught that the events amount prefix used '+'
unconditionally for any actual source, producing '+-87,00 ₽' on negative
actual amounts. Mirror the income card sign handling: '+' for positive,
Unicode '−' (U+2212) for negative, '~' for forecast (regardless of sign).

Extract a small eventAmountDisplay helper and tighten the corresponding
test assertion to require exact equality instead of substring match, so
this regression class is caught next time.

apps/frontend/src/widgets/broker-dashboard/ui/BrokerDashboard.test.tsx

@@ -362,7 +362,7 @@ describe('BrokerDashboard', () => {
 
     const [amount] = screen.getAllByTestId('dashboard-events-amount')
     expect(amount.getAttribute('data-tone')).toBe('negative')
-    expect(amount.textContent).toContain('-87,00')
+    expect(amount.textContent).toBe('−87,00 ₽')
   })
 
   it('renders events and income amounts with the ₽ symbol and no "RUB" code', () => {

apps/frontend/src/widgets/broker-dashboard/ui/BrokerDashboardEventsCard.tsx

@@ -98,6 +98,19 @@ function eventMoneyTone(event: BrokerEventItem): MoneyTone {
   return moneyTone(eventAmountValue(event), event.source)
 }
 
+function eventAmountDisplay(event: BrokerEventItem): string {
+  const amount = eventAmountValue(event)
+  if (amount === null || amount === undefined) return '—'
+  const abs = formatDashboardCurrency({
+    currency: event.currency ?? 'RUB',
+    value: Math.abs(amount),
+  })
+  if (event.source === 'forecast') return `~${abs}`
+  if (amount > 0) return `+${abs}`
+  if (amount < 0) return `−${abs}`
+  return abs
+}
+
 export function BrokerDashboardEventsCard({
   accountId,
   data,
@@ -195,14 +208,7 @@ export function BrokerDashboardEventsCard({
                     ticker: event.ticker,
                     name: event.name,
                   })
-                  const amount = eventAmountValue(event)
+                  const formattedAmount = eventAmountDisplay(event)
-                  const formattedAmount =
-                    amount === null || amount === undefined
-                      ? '—'
-                      : `${event.source === 'actual' ? '+' : '~'}${formatDashboardCurrency({
-                          currency: event.currency ?? 'RUB',
-                          value: amount,
-                        })}`
                   return (
                     <Box component="tr" key={event.id} data-testid="dashboard-events-row">
                       <Box component="td" sx={TD_SX_LEFT}>