Add per-UTXO lock and unlock controls to Manage UTXOs

[praveenperera]

Parent issue: #168

Summary

Add per-outpoint lock and unlock controls to the Manage UTXOs advanced flow.

This is the canonical fine-grained UI for managing locked UTXOs.

Scope

• add per-row lock and unlock controls for individual UTXOs
• visibly indicate lock state in the UTXO list
• keep the UI scoped to individual outpoints, not transaction-level bulk actions
• ensure the flow stays consistent with backend enforcement so locked outputs are not presented as normally spendable

Out of scope

• transaction-details bulk lock/unlock
• BIP329 import/export sync
• backend send enforcement itself

Acceptance criteria

• a user can lock an individual UTXO from Manage UTXOs
• a user can unlock an individual UTXO from Manage UTXOs
• locked UTXOs are clearly identifiable in the list
• the screen stays in sync with backend lock state after changes

Dependencies

• depends on the canonical outpoint-lock state and APIs
• should coordinate with send-enforcement behavior so the UI matches actual spend rules