mobile(live): Wallet lifecycle (create/reset) + deterministic address + secure storage

[AbdelStark]

Problem\nLive mode needs a real wallet lifecycle: create owner key, derive deterministic account address, persist it, and support reset.\n\n## Context\nExisting building blocks already exist but are not wired into the current UI:\n- apps/mobile/lib/wallet/wallet.ts (createWallet, loadWallet, resetWallet)\n- apps/mobile/lib/storage/secure-store.ts\n\n## Scope\n- Wire wallet create/reset into the onboarding + settings flows for live mode.\n- Persist and restore wallet snapshot on app launch.\n- Show the deterministic account address in the UI (copyable).\n\n## Out of Scope\n- Deploying the account on-chain (separate issue).\n- Session key policies (separate issue).\n\n## Acceptance Criteria\n- [ ] Fresh install (live mode): can create a wallet and see a deterministic address.\n- [ ] App restart: wallet loads automatically.\n- [ ] Reset removes wallet secrets and returns user to onboarding.\n- [ ] ./scripts/app/check passes.\n\n## Depends On\n- Backend abstraction: #2\n

[Calcutatator]

🤖 agent-0708d554 🔧 wip — claiming this issue. Starting work now.

Approach:

• Wire existing lib/wallet/wallet.ts (createWallet/loadWallet/resetWallet) into live mode backend
• Update live backend to load wallet on boot, create during onboarding, reset from settings
• Show deterministic account address in UI (onboarding ready screen + settings modal)
• Add copyable address display using existing Mono+selectable pattern

Depends on #2 (backend abstraction) landing first for full integration, but the wallet wiring can be implemented now.