fix(ContractorPayments): restore hours input typing + live hint updates

[aaronlee777]

Summary

• Follow-up to refactor(ContractorPayments): replace total tally with live hourly pay hint #2241. The hours input in the edit-contractor-payment modal was dropping typed characters and the live pay hint wasn't updating on arrow-key commits.
• Root cause: refactor(ContractorPayments): replace total tally with live hourly pay hint #2241 attached an onChange handler directly to the <Input> slot inside react-aria's <NumberField>, which replaced react-aria's context-injected handler that controls the displayed text and value commits.
• Fix: move the onChange callback up onto <Group> so React's synthetic-event bubbling observes the same events without overriding react-aria's handler. Drive the hint from a useState<number> fed by onInputChange (per-keystroke) + onChange (arrow keys / step buttons).
• Hint stays live; the inner <Input> is back under react-aria's control.

Test plan

• Open the edit-payment modal for an hourly contractor — typing into Hours updates the field and the hint live, character-by-character.
• Press ↑ / ↓ — Hours steps and the hint updates with each step.
• Open the modal for a fixed-wage contractor — no hint, no Hours field.
• Hint hides when no hourly rate is set on the contractor.
• Submit — hours reaches the payload unchanged.
• Regression sanity in Storybook: type into any other NumberInput story — no dropped characters.

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