feat(account): phone sign-in, code verification and the account screen

[roncodes]

Stacked on #74. Redesigns sign-in, sign-up, code verification and the account screen to match the prototype.

Sign in and sign up

• One phone-first screen for both. Sign-up adds a name field.
• The country picker is a searchable sheet. It defaults to defaultCountry from the storefront config, then the device region.
• Invalid numbers and failed sends show inline errors.
• Apple, Google and Facebook buttons appear only when the build enables them.
• Terms and privacy links appear when termsUrl / privacyUrl are configured.
• Coming from checkout, the copy changes to "Sign in to place your order", and the customer goes straight back to checkout once verified. Before, they were left on the Profile tab.

Code verification

• One screen covers sign-in, sign-up, adding a phone and confirming account deletion:
  • six boxes, backed by one hidden field, so paste and SMS autofill work;
  • auto-submits on the last digit;
  • inline "code didn't match" error, which clears the boxes;
  • "Change number" link and a 30-second resend timer.
• Adding a phone is now a clear two-step flow: enter the number, then verify it.

Account screen

• Profile header with Edit, plus a prompt to add a phone number when it's missing. This replaces the action sheet that used to pop up on every visit.
• An active-order card that opens tracking.
• Links to Orders, Offers, Saved places, Payment methods (Stripe only) and Notifications (with the unread count).
• Language and appearance pickers, and Terms and Privacy links.
• Sign out, and Delete account behind a confirmation sheet that sends the code.

Other

• Route names are unchanged. Login, CreateAccount and Profile resolve to the new screens through the screen registry. The old login, verify, add-phone and profile screens are removed.
• Web fix: the native Google Sign-In package crashed the web bundle as soon as the sign-in screen was imported. It now has a web shim, like the other native-only modules, and the Google button is hidden on web.
• Auth and Account strings added in English, Mongolian and Ukrainian.

Checks

• yarn jest: 192 passing, including new tests for the redirect hand-off and the Google Sign-In shim.
• yarn typecheck:strict and yarn lint:strict pass with no errors.
• Checked on web at phone width:
  • sign-in from checkout;
  • code entry, with the wrong-code error and resend;
  • the account screen with a test customer, plus the appearance and delete sheets.
• Not tested live: completing a real sign-in, since the local API has no SMS provider.

Known issue (not from this PR)

On web, choosing Light while the device is in dark mode (or the reverse) leaves themed colours empty. The theme CSS only defines its variables inside prefers-color-scheme media queries. The appearance picker makes this easier to hit, so it's being fixed separately in the theme CSS post-processing.