As a user, I want to sign in with my Google account, so that I can get started in one tap

✅ Shipped in Sprint 1. Kept here as a worked example of a completed story.

Acceptance criteria

• Given I am on the sign-in screen, when I select "Continue with Google", then the Google account chooser appears
• Given I pick an account, when authorization completes, then I am signed in and my profile is populated
• Given an account already exists with the same email, when I sign in with Google, then the accounts are linked, not duplicated
• Given I am offline, when I attempt sign-in, then I see a clear retry message rather than a spinner

Definition of Done

• Acceptance criteria pass
• Account linking tested against an existing email
• Code reviewed and merged
• Tests written and green
• Accepted by Product Owner