feat(ui): Add thousands separator formatting to item amount input

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Summary

Replace the type="number" input with a type="text" input for the item
amount field in InventoryControl, and apply comma-separated thousands
formatting (e.g. 1,000, 10,000) using toLocaleString('en-us').

Changes

• Changed input type from number to text
• Format the entered value with thousands separators on each keystroke
• Preserve cursor position after formatting using useRef and useEffect
• Strip non-numeric characters before dispatching the value to the Redux store

Motivation

The default number input does not display thousand separators, making it
difficult to read large quantities at a glance. This change improves
readability without affecting the underlying numeric value stored in state.

Testing

• Type a large number (e.g. 1000000) and verify it displays as 1,000,000
• Verify the cursor does not jump to the end while editing mid-value
• Verify that the dispatched amount is correct (no commas included)
• Verify that empty input resets the amount to 0

Demo