Feature request: local alias book for Silent Payment recipients

[semillabitcoin]

Summary

Add a local alias book exclusively for Silent Payment addresses, allowing users to associate a human-readable name with every sp1... they want to reuse as a recipient.

Motivation

SP addresses are ~117 characters in bech32m and visually indistinguishable from each other. When someone sends you their sp1..., or you obtain it from a website or any other medium, there is currently no way in Sparrow to:

• save it under a name ("Alice", "Bob")
• verify at a glance that the address pasted into Send matches the one stored months ago
• avoid having to request or look it up again each time

Why this does not overlap with existing solutions

vs. issue #511 (closed): the stated reason for closing was "encourages address reuse, unconditionally bad". That argument does not apply to SP by design: the sender derives a fresh output on every payment from the same sp1.... There is no onchain address reuse.

UX benefit

A local alias reduces the risk of sending to the wrong destination: instead of comparing two near-identical sp1... strings, the user picks "Alice" from a list and confirms the recipient is correct before signing.

Proposed minimum scope

• A "Silent Payment Contacts" tab/section inside the wallet (SP wallets only)
• Basic CRUD: add, rename, delete
• Autocomplete in the Pay to field of the send dialog when the user starts typing an alias
• Persistence inside the wallet file, with an optional password-based encryption option