Submit button doesn't work if the keyboard is on the screen.

[wchancao]

Describe the bug
Submit button doesn't work if the keyboard is on the screen.

To Reproduce

1. Take a buy order
2. Input the invoice
3. Clicking the submit button does nothing if the keyboard is on the screen

Expected behavior
Clicking the submit button should send the invoice

Smartphone (please complete the following information):

• Device: Google Pixel 8a
• OS: Android 16
• Mostro v1.2.9

[codaMW]

Traced this to the invoice form overflowing when the keyboard shrinks the viewport, which clips the Submit button's tap area. Opened #636 with a fix (SingleChildScrollView wrap). It didn't reproduce on my own device (viewport-specific), so @wchancao could you confirm it resolves on your Pixel 8a?

[wchancao]

Same behavior in v1.3.0, but not sure if the fix was included in that version