[Gaubee]

Summary

Migrates AmountInput component to use native Amount type instead of strings.

Breaking Changes

• value: Amount | null (was string)
• onChange: (Amount | null) => void (was string => void)
• balance: Amount (was string)
• max: Amount (was string)

Changes

• AmountInput component: Now works natively with Amount objects
  • Internal string state for input display
  • Parses user input to Amount on every keystroke
  • Validates against decimals precision automatically
  • Derives decimals/symbol from balance Amount when available
• useSend hook: state.amount is now Amount | null
• SendPage: Integrated with new AmountInput API
• Tests: Updated all test files with Amount objects
• Stories: Updated to demonstrate Amount usage

Benefits

• Type-safe amount handling end-to-end
• No more string parsing at component boundaries
• Automatic precision validation
• Cleaner API that matches the Amount type system

Closes #65