[PM-40519] feat: Add SDK-backed passkey foundation services to TestHarness

[morganzellers-bw]

🎟️ Tracking

PM-40519

📔 Objective

Adds SDK-backed passkey test scenarios to TestHarness.

• Adds the Core/Autofill/SDK+ layer, which drives BitwardenSdk's Fido2 client directly (makeCredential/getAssertion) the same way the main app and AutoFill extension do, instead of delegating to the OS passkey UI.
• SDKPasskeyService lazily bootstraps a BitwardenSdk.Client backed by a synthetic identity persisted in the Keychain, so registered credentials survive relaunches.
• SDKFido2CredentialStore/SDKFido2UserInterface satisfy the SDK's Fido2CredentialStore/Fido2UserInterface protocols; SDKCipherStorageService persists registered credentials across app launches.
• No UI wiring yet — this PR lands the service layer standalone, fully covered by its own test suite. The next PR in the stack adds the "Register Passkey (SDK)" screen that consumes it.

---

Stack: #2945 → #2946 → #2947 → #2948

[github-actions]

🤖 Bitwarden Claude Code Review

Overall Assessment: APPROVE

Re-reviewed the full TestHarnessShared/Core/Autofill/Passkey layer at 8ed6220, covering DefaultPasskeyService, DefaultFido2CredentialStore, DefaultFido2UserInterface, DefaultCipherStorageService, StoredCipher, the keychain-backed SyntheticIdentity, and the XcodeGen/Sourcery wiring. All previously raised findings are addressed: session() now caches the bootstrap as a Task, saveCredential replaces by cipher ID instead of appending duplicates, findCredentials honors the SDK-supplied ids/userHandle filters, and loadOrCreateIdentity() clears persisted ciphers when a new identity is minted (with a regression test simulating a lost keychain identity). Secret material stays in the Keychain and only SDK ciphertext lands in UserDefaults, consistent with the zero-knowledge rules; the new code is confined to the test harness target and adds no production surface.

Code Review Details

No findings at or above the reporting threshold.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79.46%. Comparing base (7d9c4a7) to head (8ed6220).

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #2945       +/-   ##
===========================================
+ Coverage   39.58%   79.46%   +39.87%     
===========================================
  Files         363     1172      +809     
  Lines       17106    75144    +58038     
===========================================
+ Hits         6772    59710    +52938     
- Misses      10334    15434     +5100     

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