Autofill category from the payee's last transaction

When you enter a transaction for a payee you've used before, the category field pre-fills with whatever you assigned that payee last time.

It behaves exactly like an Autofill rule: the field is pre-filled in the Add Transaction form.

Details:

• Looks at the most recent transaction with a matching payee and pre-fills its category.
• Explicit Autofill rules always take precedence. If a rule matches the payee, the rule wins.
• Applies to manual entry only, imports are handled by Continuous rules as they are today.
• Falls back to an empty field when the payee is new or has no category history.
• Toggle in Settings, on by default.
• Should have different visual cues then existing autofill rules