[Eco Bounty] IoTex Hub Numeric Input Field Accepts Alphabetical Characters

Description: The amount input field on the Buy page does not have restricted input types. Users are able to type or paste alphabetical characters (letters) into the field. This causes the "You will receive" estimate at the bottom to mirror the invalid text string instead of a numerical calculation.

Steps to Reproduce:

1. Navigate to hub.iotex.io/buy-iotx/crypto.

2. Tap on the "How much IOTX you want to buy" input field.

3. Type letters (e.g., "gjjxxhknknb") instead of numbers.

4. Observe the input field and the "You will receive" summary text.

Expected Result: The input field should be restricted to numerical values and decimals only (type="number" or inputmode="decimal"). Alphabetical characters should be ignored or blocked.

Actual Result: The field accepts alphabetical strings, and the UI attempts to process them as a valid amount in the summary footer.

Wallet Address: io1tkw393kejmxwnd454twc6020sxcyvh5dxqmren

Device & Environment:

-Operating system: Android 13

-Device model: Redmi Note 10 Pro