feat: add batch transfer modal for multi-wallet key distributions

[onajidavid87-web]

Summary

• Added a Batch Transfer option to the portfolio holding row action menu (PortfolioHoldingRow).
• Created BatchTransferModal allowing holders to send creator keys to multiple wallets in a single signed transaction.
• Supports a dynamic list of up to 10 recipient rows (Stellar wallet address + key quantity).
• Automatically disables the "Add Recipient" button when 10 rows are reached.
• Computes and displays total keys to transfer in real time as quantities change.
• Validates wallet addresses and quantities with row-level error messages.
• Disables submit and displays an error if the total quantity exceeds the available liquid balance.
• Wired up submission to the batch_transfer contract function with useBatchTransferMutation and optimistic updates.

Testing

• pnpm lint
• pnpm build
• pnpm vitest run src/utils/__tests__/batchTransfer.utils.test.ts (15/15 passed)
• pnpm vitest run src/components/common/__tests__/BatchTransferModal.test.tsx (12/12 passed)
• pnpm vitest run src/components/common/__tests__/PortfolioHoldingRow.batchTransfer.test.tsx (7/7 passed)
• pnpm vitest run src/services/__tests__/creatorKeysContract.service.test.ts (4/4 passed)

Checklist

• Linked issue or backlog item
• Scope is limited to the stated change
• Updated docs if behavior or setup changed
• Added screenshots for UI changes when relevant

Closes #831

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