feat(accounts): multi-account support — switcher, add-account flow with recovery choice

[0xnullifier]

What

Multi-account support on the home view:

• Balance card: account chip (Account N · address) with a chevron opens the account switcher; a standalone copy icon keeps address copying; a new "+" button starts the add-account flow.
• Accounts drawer: now lists all accounts (tap to switch, optimistic with rollback), plus the card-color picker, Settings, and an enabled Add Account entry.
• Add-account drawer (two steps): Public creates a WalletType.OnChain account immediately; Private swaps to a recovery-choice step — Guardian (routes to the operator picker at /add-account/guardian) or Fully Private (routes to /add-account/private).
• Local-risk acknowledgment (/add-account/private): three sequential screens, each stating one consequence of a guardian-less account (device loss = permanent fund loss even with the seed phrase saved), each with an "I understand" primary CTA and a "Use a Guardian instead" escape hatch. The final confirm creates the OffChain account.
• New accounts are auto-named "Account N" and become the active account on creation.

Plumbing

• CreateAccountRequest carries an optional guardianEndpoint, threaded through both dispatchers → Actions.createHDAccount → Vault.createHDAccount; an explicitly chosen endpoint wins over the guardian-sibling default.
• ChooseGuardianScreen gains a submitLoading prop (spinner + re-tap guard on Continue) for callers that create in place.

Testing

• yarn tsc --noEmit clean; yarn lint:i18n clean.
• src/components/ui suites pass (AccountsDrawer tests updated for the switch list; barrel test covers the new drawer).
• Manual walkthrough of all three create paths still pending on a device build.