Multiple account support

[sepehr-safari]

What

Let one Signet instance hold and serve more than one key.

Why

Signet currently manages a single key (one NIP-49-encrypted blob at rest). People routinely keep separate identities — personal, work, a bot — and want one signer for all of them instead of running several.

Shape

Each account carries its own:

• NIP-49-encrypted key at rest
• pubkey + bunker:// URI
• relay set
• authorization policy (method + event-kind allowlists)

Daemon:

• Store N encrypted key blobs (migration: the current single key becomes account feat: relay listen/sign loop over NIP-46 #1).
• Route each incoming NIP-46 request to the account whose pubkey it addresses.
• Serve loop subscribes for every account's pubkey across the union of their relays.

GUI:

• Account list: add / import / remove / switch.
• Per-account bunker URI + relay status on the serving screen.

Notes

• NIP-46 requests are addressed to a specific remote-signer pubkey, so routing is a lookup by recipient pubkey — no ambiguity.
• Decide whether relay sets are per-account or shared: per-account is more flexible but means more concurrent subscriptions.