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.
Sergey Krylov
94f8bb876d