feat(machine): source LNbits transport from the pairing seed, not just env

Completes the consumer half of bitspire-#70: a paired machine gets its LNbits
transport relay(s) + server pubkey from the pairing, so a blank-.env unit reaches
the backend after scanning a seed — no VITE_RELAY_URL / VITE_LNBITS_SERVER_PUBKEY
provisioning.

- resolveSigner now returns { signer, transport }. transport (relays +
  lnbitsServerPubkey) comes from the seed on a fresh pair / seeded resume, and
  from the binding on a seedless resume. It's threaded out of resolveSigner
  rather than re-parsed in loadLightningConfig because the seed arrives over the
  one-shot get-atm-secrets IPC — a second consumer would break that contract.
- bunker_binding persists relays + lnbits_server_pubkey (state.db v11→v12,
  nullable so pre-#70 bindings resume and fall back to env). Mirrored into
  BunkerBindingRecord (preload + electron.d.ts).
- initializeLightningServices resolves effective transport with env-wins
  precedence (explicit env override for dev, else pairing, else a dev-only
  localhost relay), mutating CONFIG to a single source of truth and building the
  Nostr/LNbits/CLINK clients from the full relay list. Strict + required-config
  validation now run on the resolved values.

state.db round-trip test covers the new columns + their absence on a pre-#70
binding. Renderer + electron typechecks and all 38 machine tests pass.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

apps/machine/electron/preload.ts

@@ -51,6 +51,10 @@ export interface BunkerBindingRecord {
   bunkerUrl: string
   seedFingerprint: string
   pairedAt: number
+  /** LNbits transport relays from the seed (#70); absent on pre-#70 bindings. */
+  relays?: string[]
+  /** LNbits nostr-transport server pubkey (hex) from the seed (#70). */
+  lnbitsServerPubkey?: string
 }
 
 /**