[ex3ndr]

Claude providers are setup-token only (Steve's rule; prod returns claudeSignIn: false). Android removed the same branch in #2019.

• The chooser entry says "Use a Claude setup token", matching web. It used to say "Sign in with Claude". The string constant is renamed to claudeSetupToken. The entry appears only when the server offers setup tokens.
• ClaudeSignInViewController is now the setup token alone: the hint and a prominent "Add setup token" button. Its browser branch is gone: Open Claude, the code field, start/watch/send, and the Claude finish/cancel calls. It no longer depends on the server's claudeSignIn flag. ChatGPT's sign-in is unchanged.
• Tests:
  • The hosted HostedProvidersTests fixture is now a setup-token server. Its Claude test asserts no open button or code field and attaches a screenshot.
  • The live HappyCloudUITests.testGProviders… expects the token-only screen.
• docs/SERVER-SIGN-IN.md is updated.

Verified:

• Live, against the prod QA server qa-batch-76eca2 on the simulator, before and after removing the branch: the chooser and the Claude screen each show only the setup token.
• HostedProvidersTests 7/7 on the simulator, and 7/7 on the iPhone 12 at the first commit, which is where the screenshot comes from.
• HappyCore's finishCloudSignIn API binding remains, unused by the UI.

[ex3ndr]

Merge note for hosted CI run 42562470287. uikit passed on both attempts.

• Waiver: HostedMediaDownloadTests.testASmallPhotoDownloadsByItself (line 383, "timed out" after 14.7s) failed on attempt 1. It isn't in the failed logs of the previous 11 happy-ios runs. On the Mac simulator it passed 10/10 at this head (b1a1636), and it passed on the rerun (attempt 2, 0.07s). This PR changes only the providers UI, strings, provider tests and docs.
• Every other failure is known or has failed before:
  • Known: InstantSignOut 318, SystemMonitor 332/334, NavigationTiming 152, ThumbHash 212, ChatNavigation testHowLongAChatTakesToOpen.
  • Seen before: AttachPreview video 114/229 (accepted as a CI flake; main hosted3 post-labels), AttachGesture 539, SendFlight 315–319 (run 42545656127), ChatNavigation 281 (fix(ios): repair pairing and media reconnect; isolate UI test readiness #2000), ChatProfile 314 (fix(ios): discard connection snapshots after page hide #2010).