Add Playwright e2e test for the in-app wallet balance top-up prompt on insufficient balance

[Chuks-coderr]

Overview

The wallet balance top-up prompt must appear when the user's balance is insufficient for stream creation and dismiss when balance becomes sufficient. An e2e test would verify this flow.

Proposed Solution

• Mock the wallet balance at a value less than the stream amount
• Attempt to submit the create-stream form
• Assert the top-up banner appears with the correct shortfall amount
• Update mock balance to sufficient → assert banner dismisses

Acceptance Criteria

• Banner appears with correct shortfall when balance is insufficient
• Banner dismisses when balance becomes sufficient
• Submit button remains disabled while balance is insufficient
• No banner shown when balance is sufficient from the start