feat: implement Send Money page

[dzekojohn4]

Task

Create src/app/send/page.tsx.

Form fields

• Recipient Stellar address (text input)
• Amount (number input)
• Asset selector (XLM or USDC)
• Submit button

Validation (Zod)

z.object({
  recipient: z.string().min(56).max(56),
  amount: z.string().regex(/^\d+(\.\d+)?$/),
  asset: z.enum(['XLM', 'USDC']),
})

Behaviour

• On submit: call useTransactions.sendMoney()
• Show success toast and redirect to /history on success
• Show error toast on failure
• Loading state on submit button

Acceptance Criteria

• Validation errors shown inline
• Success redirects to /history
• Error toast shown on API failure