fix(ui): seed QRs use the SeedQR standard so hardware wallets can scan them

Plain-text seed QRs didn't scan into Passport Prime — wallets that
import seeds by QR (Passport, SeedSigner, Keystone, Nunchuk, Sparrow)
expect the SeedQR standard: each BIP39 word as its zero-padded 4-digit
wordlist index, concatenated into a numeric QR.

- new utils/seedqr.ts encodes BIP39 words per the SeedSigner spec
  (@scure/bip39 wordlist; vector-checked abandon=0000, zoo=2047)
- new shared SeedRevealPanel (Words/QR tabs, tap-to-reveal blur) now
  backs the LND reveal AND the Settings→Backup recovery-phrase reveal,
  so every current and future seed reveal behaves the same
- onboarding seed + Settings reveal: QR defaults to SeedQR with a
  plain-text toggle
- LND seed stays plain-text-only with an explicit note: aezeed is not
  BIP39 and only restores into LND-based wallets (Zeus/Blixt/another
  node) — SeedQR-encoding it would just mislead

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

neode-ui/package.json

@@ -24,6 +24,7 @@
     "generate-welcome-speech": "node scripts/generate-welcome-speech.js"
   },
   "dependencies": {
+    "@scure/bip39": "^2.2.0",
     "@types/dompurify": "^3.0.5",
     "@vue-leaflet/vue-leaflet": "^0.10.1",
     "buffer": "^6.0.3",