feat: BIP-39 master seed for unified key derivation

Replace fragmented random key generation with a single 24-word BIP-39
mnemonic that deterministically derives all node keys: Ed25519 (DID),
secp256k1 (Nostr/Bitcoin), BIP-84 xprv (Bitcoin Core), and LND aezeed
entropy. New onboarding flow: seed generate → word verification → identity
naming. Restore path enabled via 24-word entry. Includes seed RPC handlers,
mock backend support, LND/Bitcoin Core wallet-from-seed integration, and
UI polish across settings and discover views.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

core/archipelago/src/api/rpc/dispatcher.rs

@@ -22,6 +22,13 @@ impl RpcHandler {
             "auth.isOnboardingComplete" => self.handle_auth_is_onboarding_complete().await,
             "auth.resetOnboarding" => self.handle_auth_reset_onboarding(params).await,
 
+            // Seed management (BIP-39 mnemonic)
+            "seed.generate" => self.handle_seed_generate().await,
+            "seed.verify" => self.handle_seed_verify(params).await,
+            "seed.restore" => self.handle_seed_restore(params).await,
+            "seed.save-encrypted" => self.handle_seed_save_encrypted(params).await,
+            "seed.status" => self.handle_seed_status().await,
+
             // Container orchestration (for Archipelago-managed containers)
             "container-install" => self.handle_container_install(params).await,
             "container-start" => self.handle_container_start(params).await,
@@ -78,6 +85,7 @@ impl RpcHandler {
 
             // Bitcoin & Lightning deep data
             "bitcoin.getinfo" => self.handle_bitcoin_getinfo().await,
+            "bitcoin.init-wallet-from-seed" => self.handle_bitcoin_init_wallet_from_seed(params).await,
             "lnd.getinfo" => self.handle_lnd_getinfo().await,
             "lnd.listchannels" => self.handle_lnd_listchannels().await,
             "lnd.openchannel" => self.handle_lnd_openchannel(params).await,
@@ -92,6 +100,7 @@ impl RpcHandler {
             "lnd.gettransactions" => self.handle_lnd_gettransactions().await,
             "lnd.connect-info" => self.handle_lnd_connect_info().await,
             "lnd.export-channel-backup" => self.handle_lnd_export_channel_backup().await,
+            "lnd.init-wallet-from-seed" => self.handle_lnd_init_wallet_from_seed(params).await,
 
             // Multi-identity management
             "identity.list" => self.handle_identity_list(params).await,