[DRAFT]: FiatStrategy PoC implementation

[OGPoyraz]

• Added new strategy enum: TransactionPayStrategy.Fiat.
• Added fiat marker on controller state: TransactionData.fiatPayment?: FiatPaymentData.
• Added controller method/action: TransactionPayController.setFiatPayment(transactionId, fiatPayment).
  • When fiatPayment is set, it clears token-based fields (paymentToken, sourceAmounts, quotes, totals, etc.) and stops loading.
• Added FiatStrategy:
  • getQuotes() logs fiat-strategy and returns a single mock quote (provider fee = 2% of required token USD sum).
  • execute() waits ~30s, then returns a deterministic mock hash.
• Integrated strategy resolution via getStrategyByName().