fix(batch): reject duplicate recipient addresses and prevent floating-point total drift (#13)

[ghzhost]

Summary

Enforces cross-row recipient validation and exact integer stroop total calculation for batch payments.

Closes #13.

Changes

1. Duplicate Recipient Detection:
   • Added superRefine on batchSchema in BatchForm.tsx to detect duplicate destination addresses across batch items and attach path-specific validation errors directly under the duplicate recipient row.
2. Self-Send Warning:
   • Passed connected wallet publicKey from useWallet() to BatchForm to display an inline non-blocking warning when any recipient matches the connected account.
3. Integer Stroop Total Calculation:
   • Introduced parseAmountToStroops, xlmToStroops, stroopsToXlm, and calculateBatchTotal in src/lib/stellar.ts to compute batch payment sums via exact BigInt stroop arithmetic (7 decimal places) instead of naive parseFloat additions.
   • Updated BatchForm and useBatchPayment to use calculateBatchTotal, preventing floating-point precision drift across many decimal rows.
4. Test Coverage:
   • Added tests in BatchForm.test.tsx for:
     • Disabling submission and flagging errors on duplicate recipient addresses.
     • Warning on self-send when a recipient matches senderPublicKey.
     • Validating total calculations across 100 small rows (e.g. 0.0000001 XLM) without floating point drift.

Verification

• NODE_ENV=test pnpm test: 27 test files, 116 passed (100% green).
• pnpm build: Completed successfully with clean Vite bundle.