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/router/index.ts

@@ -35,6 +35,21 @@ const router = createRouter({
           name: 'onboarding-path',
           component: () => import('../views/OnboardingPath.vue'),
         },
+        {
+          path: 'onboarding/seed',
+          name: 'onboarding-seed',
+          component: () => import('../views/OnboardingSeedGenerate.vue'),
+        },
+        {
+          path: 'onboarding/seed-verify',
+          name: 'onboarding-seed-verify',
+          component: () => import('../views/OnboardingSeedVerify.vue'),
+        },
+        {
+          path: 'onboarding/seed-restore',
+          name: 'onboarding-seed-restore',
+          component: () => import('../views/OnboardingSeedRestore.vue'),
+        },
         {
           path: 'onboarding/did',
           name: 'onboarding-did',