Show sign-in progress step by step instead of one indefinite spinner

[wparad]

Summary

• After returning from the Authress-hosted login page, the app just showed a spinner with no indication of what was happening — and no way to tell what state it was stuck in if something stalled. MainActivity also fire-and-forgets completeAuthenticationRequest's Result, so a failure there previously left the spinner running forever with nothing surfaced to the user.
• AuthressLoginClient now exposes authStatus (Idle / OpeningBrowser / AwaitingRedirect / CompletingSignIn) and authError state flows, updated at every transition and on every failure path in authenticate() and completeAuthenticationRequest().
• LoginScreen renders these as an ordered checklist — opening the sign-in page, waiting on the browser, completing sign-in, loading the mailbox — with the active step spinning, completed steps checked off, and the failure message (if any) shown directly instead of an indefinite spin.
• If a step runs long, a "this is taking longer than expected" hint appears with a "Try again" action. Waiting on the user in the browser gets a much longer grace period than the Authress network calls, since that step is expected to take a while.

Test plan

• Manual: tap Continue, complete sign-in in the browser, confirm each step checks off and the mailbox loads
• Manual: force a failure (e.g. airplane mode) during sign-in and confirm the error message and step list surface instead of an indefinite spinner
• Could not run the app in this environment (no Android SDK), so this is reviewed manually

🤖 Generated with Claude Code

https://claude.ai/code/session_01XRMBgZXVCEVwBuBWapy5J7

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