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>

neode-ui/src/views/settings/InterfaceModeSection.vue

@@ -42,7 +42,7 @@ async function changeLocale(code: string) {
   <div class="glass-card px-6 py-6 mb-6">
     <h2 class="text-xl font-semibold text-white/96 mb-2">{{ t('settings.interfaceMode') }}</h2>
     <p class="text-sm text-white/60 mb-6">{{ t('settings.interfaceModeDesc') }}</p>
-    <div class="grid grid-cols-1 md:grid-cols-3 gap-4">
+    <div data-controller-container tabindex="0" class="grid grid-cols-1 md:grid-cols-3 gap-4">
       <button
         v-for="m in interfaceModes"
         :key="m.id"