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/OnboardingOptions.vue

@@ -33,8 +33,12 @@
           </p>
         </button>
 
-        <!-- Restore Backup (Coming Soon) -->
-        <div class="path-option-card text-center opacity-40 cursor-not-allowed">
+        <!-- Restore from Seed -->
+        <button
+          @click="selectOption('restore')"
+          class="path-option-card text-center"
+          :class="{ 'path-option-card--selected': selected === 'restore' }"
+        >
           <div class="mb-3 sm:mb-4">
             <div class="w-12 h-12 sm:w-16 sm:h-16 mx-auto bg-white/10 rounded-full flex items-center justify-center">
               <svg class="w-6 h-6 sm:w-8 sm:h-8 text-white/60" fill="none" stroke="currentColor" viewBox="0 0 24 24">
@@ -42,12 +46,11 @@
               </svg>
             </div>
           </div>
-          <h3 class="text-lg sm:text-xl font-semibold text-white mb-1 sm:mb-2">Restore Backup</h3>
+          <h3 class="text-lg sm:text-xl font-semibold text-white mb-1 sm:mb-2">Restore from Seed</h3>
           <p class="text-white/70 text-xs sm:text-sm">
-            Restore from a previous backup
+            Enter your 24-word recovery phrase
           </p>
-          <span class="text-xs text-white/50 mt-1 block">(Coming Soon)</span>
-        </div>
+        </button>
 
         <!-- Connect Existing (Coming Soon) -->
         <div class="path-option-card text-center opacity-40 cursor-not-allowed">
@@ -81,7 +84,6 @@
 <script setup lang="ts">
 import { ref, onMounted } from 'vue'
 import { useRouter } from 'vue-router'
-import { completeOnboarding } from '@/composables/useOnboarding'
 import { playNavSound } from '@/composables/useNavSounds'
 
 const router = useRouter()
@@ -96,12 +98,11 @@ function selectOption(option: string) {
 }
 
 async function proceed() {
-  try {
-    await completeOnboarding()
-  } catch (e) {
-    if (import.meta.env.DEV) console.warn('completeOnboarding failed, localStorage fallback ensures onboarding is marked complete', e)
-  }
   playNavSound('action')
-  router.push('/login').catch(() => {})
+  if (selected.value === 'restore') {
+    router.push('/onboarding/seed-restore').catch(() => {})
+  } else {
+    router.push('/onboarding/seed').catch(() => {})
+  }
 }
 </script>