[PM-27135] feat: Add Use Passkey screen

[morganzellers-bw]

🎟️ Tracking

PM-27135

📔 Objective

Third PR in a 4-PR stack adding SDK-backed passkey test scenarios to TestHarness. Stacked on #2946.

• Adds the "Use Passkey (SDK)" scenario: lists credentials registered via SDKPasskeyService.registeredCredentials, and asserts against the tapped credential's specific credential ID and relying party ID via SDKPasskeyService.assertPasskey, showing the resulting relying party ID and username.
• Wires the new screen into the scenario picker and root navigation.

📸 Screenshots

---

Stack: #2945 → #2946 → #2947 → #2948

[github-actions]

🤖 Bitwarden Claude Code Review

Overall Assessment: APPROVE

This PR adds the "Use Passkey" TestHarness scenario: it lists SDK-registered credentials via PasskeyService.registeredCredentials() and asserts against the tapped credential's specific credential ID and relying party ID via PasskeyService.assertPasskey(credentialId:rpId:). Reviewed the new UsePasskey processor/state/view/action/effect files and their tests, the GetAssertionResult fixture, the RootCoordinator/RootRoute/ScenarioPickerState wiring, and the added localization strings. The implementation mirrors the existing RegisterPasskey sibling pattern (unidirectional flow, StateProcessor, AutoMockable-backed tests), every new localization key is referenced by code, the fixture matches the SDK initializer and stays confined to the Fixtures/ path excluded from the app target, and the loading-state, duplicate showScenarioPicker(), and unused PasskeyAutofill key findings from earlier in this PR's history are resolved in the current diff.

Code Review Details

No new findings met the confidence threshold for reporting.

PR Metadata Assessment

• ❓ QUESTION: The Screenshots section is still a placeholder comment; please attach captures of the new screen's loading, empty, success, and failure states before merge.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79.49%. Comparing base (c27001f) to head (0064e31).

Additional details and impacted files

@@                              Coverage Diff                              @@
##           pm-27134-testharness-register-passkeys-ui    #2947      +/-   ##
=============================================================================
- Coverage                                      79.50%   79.49%   -0.02%     
=============================================================================
  Files                                           1169     1169              
  Lines                                          75028    75028              
=============================================================================
- Hits                                           59652    59644       -8     
- Misses                                         15376    15384       +8     

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[github-actions]

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