Add auth E2E tests and wire Linux/Windows CI

[atavism]

Closes https://github.com/getlantern/engineering/issues/3057

[Copilot]

Pull request overview

Adds cross-platform (Linux/Windows) auth UI smoke coverage and tightens logout/session clearing behavior to support reliable E2E testing and CI validation.

Changes:

• Introduces Linux/Windows integration smoke tests for key auth flows using deterministic fakes.
• Adds stable widget keys across auth/account screens to support UI automation.
• Centralizes auth/session clearing via clearAuthSessionData() and wires it into logout/delete flows.

Reviewed changes

Copilot reviewed 20 out of 20 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
test/features/auth/provider/auth_notifier_test.dart	Adds unit tests asserting AuthNotifier forwards auth calls to LanternService.
test/core/models/app_setting_auth_session_test.dart	Adds unit tests for AppSetting.clearAuthSessionData() behavior (including optional email preservation).
lib/features/home/provider/home_notifier.dart	Improves logging formatting; updates logout clearing to use centralized auth/session clearing + resets server location.
lib/features/home/provider/app_setting_notifier.dart	Adds clearAuthSessionData() helper on notifier.
lib/features/auth/sign_in_password.dart	Adds test keys for password sign-in UI elements and formatting cleanup.
lib/features/auth/sign_in_email.dart	Adds test keys for email sign-in UI elements and formatting cleanup.
lib/features/auth/create_password.dart	Adds test keys for create-password UI elements and formatting cleanup.
lib/features/auth/confirm_email.dart	Adds test keys for confirm-email UI elements and uses centralized session clearing on back-press delete cleanup.
lib/features/auth/auth_flow_test_keys.dart	New central registry of ValueKeys for auth/account UI automation.
lib/features/auth/add_email.dart	Adds test keys for signup email flow and formatting cleanup.
lib/features/account/delete_account.dart	Adds test keys and routes account deletion cleanup through homeProvider.clearLogoutData().
lib/features/account/account.dart	Adds test keys for logout/delete CTAs.
lib/core/widgets/app_pin_field.dart	Adds optional inputKey to target the underlying PIN input widget in UI tests.
lib/core/models/app_setting.dart	Adds clearAuthSessionData() to model; formatting updates to JSON serialization code.
lib/core/common/app_text_field.dart	Adds fieldKey to target the underlying TextFormField in UI tests.
integration_test/auth/windows_auth_smoke_test.dart	Windows entrypoint to run the shared auth smoke harness.
integration_test/auth/linux_auth_smoke_test.dart	Linux entrypoint to run the shared auth smoke harness.
integration_test/auth/auth_smoke_harness.dart	Shared deterministic auth smoke scenarios (sign-in success/failure, sign-up, logout, delete).
.github/workflows/build-windows.yml	Runs Windows auth integration smoke test in CI.
.github/workflows/build-linux.yml	Runs Linux auth integration smoke test in CI (xvfb + timeout handling).

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.