feat(frontend): prevent self-streaming when recipient matches sender wallet in StreamCreationWizard

[aazminu]

Description

Prevents users from creating a payment stream to their own connected Stellar wallet address in RecipientStep (frontend/src/components/stream-creation/RecipientStep.tsx), StreamCreationWizard (frontend/src/components/stream-creation/StreamCreationWizard.tsx), and frontend/src/lib/stream-validation.ts.

Type of Change

• 🐛 Bug fix (non-breaking change which fixes an issue)
• ✨ New feature (non-breaking change which adds functionality)
• 💥 Breaking change (fix or feature that would cause existing functionality to not work as expected)
• 📚 Documentation update
• 🔧 Refactoring (no functional changes)
• ⚡ Performance improvement
• 🧪 Test addition or update

Related Issues

Closes #1632
Fixes #1632
/claim #1632

Changes Made

• Updated validateRecipient and validateStreamForm in frontend/src/lib/stream-validation.ts to accept an optional senderAddress parameter and return "Recipient address cannot be the same as your connected sender wallet" when the trimmed, case-normalized recipient matches the sender wallet address.
• Updated RecipientStep (frontend/src/components/stream-creation/RecipientStep.tsx) to compare the recipient input against the connected sender wallet address and immediately display the inline validation error alert.
• Updated StreamCreationWizard (frontend/src/components/stream-creation/StreamCreationWizard.tsx) to pass walletPublicKey to RecipientStep and disable the Next button on Step 2 when recipient validation fails.
• Added unit tests in frontend/src/lib/__tests__/stream-validation.test.ts and frontend/src/__tests__/components.test.tsx covering exact, case-insensitive, and whitespace-padded self-stream detection.

Testing

Test Coverage

• Unit tests added/updated
• Integration tests added/updated
• Manual testing performed

Test Steps

1. Run npx vitest run src/lib/__tests__/stream-validation.test.ts src/__tests__/components.test.tsx src/components/stream-creation/__tests__/StreamCreationWizard.test.tsx in frontend/ (118/118 tests pass).
2. Run npx tsc --noEmit in frontend/ (0 errors).
3. Run npx eslint src/lib/stream-validation.ts src/components/stream-creation/RecipientStep.tsx src/components/stream-creation/StreamCreationWizard.tsx src/lib/__tests__/stream-validation.test.ts src/__tests__/components.test.tsx in frontend/ (0 errors, 0 warnings).

Checklist

• My code follows the project's style guidelines
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I have checked for breaking changes and documented them if applicable

Additional Notes

Payout Details

• USDT/USDC Receiving Wallet (EVM / ERC-20 / Polygon / Arbitrum / Optimism / Base / BSC): 0x9a51790aC01c54184bcFa067bC38f7F0E7C6F6B6