Activity labels: enable add and edit label from transaction details

[johnny9]

Code Gap

The QML transaction detail page displays a label only when one already exists and the field is disabled. Qt lets users add or edit address labels from transaction history. The QML Activity flow currently has no equivalent label-editing path from a transaction.

Work Needed

• Allow adding or editing the transaction address label from Activity details where the transaction has an editable address.
• Reuse the address book/wallet label update path instead of storing Activity-only labels.
• Refresh Activity rows, details, and contacts/address surfaces after label changes.
• Clearly handle transactions without editable addresses.
• Add coverage for add label, edit label, clear label, non-editable transaction, and row refresh.

Priority

v1.0 / P2 secondary Activity/contacts enhancement.