Change add funds input to number type that only accepts integers

[rbren]

Description

This PR changes the input field for adding funds on the billing page from a text input to a number input that only accepts integers.

Changes

• Changed the input type from "text" to "number" in the PaymentForm component
• Added min, max, and step attributes to ensure only integers are accepted
• Updated the SettingsInput component to support these new attributes
• Updated the validation logic to check for integers
• Updated the tests to reflect these changes

Testing

Updated existing tests to verify the new behavior.

---

To run this PR locally, use the following command:

docker run -it --rm   -p 3000:3000   -v /var/run/docker.sock:/var/run/docker.sock   --add-host host.docker.internal:host-gateway   -e SANDBOX_RUNTIME_CONTAINER_IMAGE=docker.all-hands.dev/all-hands-ai/runtime:8bfdfdd-nikolaik   --name openhands-app-8bfdfdd   docker.all-hands.dev/all-hands-ai/openhands:8bfdfdd

[malhotra5]

Nice!