[mckaragoz]

Summary

Closes #97.

Adds efficient batch user retrieval by UserKey with support for target-aware authorization policies.

Changes

• Add GetByKeysAsync() to retrieve up to 250 user summaries in a single request.
• Implement batch retrieval for EF Core and InMemory stores.
• Introduce AccessContext.TargetUserKeys for multi-target authorization.
• Extend AccessContextFactory to support batch targets.
• Enable sandbox-scoped batch authorization in Identity Lab.
• Optimize Identity Lab member retrieval to eliminate N+1 requests.
• Add regression tests for target normalization, authorization context propagation, and batch request limits.

Notes

• Uses a single .admin action without introducing a separate self endpoint.
• Existing single-target authorization behavior remains unchanged.
• Batch access remains subject to permissions and application-defined policies.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 92.67016% with 14 lines in your changes missing coverage. Please review.
✅ Project coverage is 86.76%. Comparing base (13e22f3) to head (40a69d1).

Files with missing lines	Patch %	Lines
...am.UltimateAuth.Client/Services/UAuthUserClient.cs	0.00%	8 Missing ⚠️
...s.InMemory/Stores/InMemoryUserSummaryQueryStore.cs	96.00%	1 Missing and 1 partial ⚠️
...h.Users.Reference/Endpoints/UserEndpointHandler.cs	90.90%	1 Missing and 1 partial ⚠️
...mateAuth.Core/Contracts/Authority/AccessContext.cs	85.71%	1 Missing ⚠️
...Users.Reference/Services/UserApplicationService.cs	96.15%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##              dev     #113      +/-   ##
==========================================
+ Coverage   86.71%   86.76%   +0.05%     
==========================================
  Files         678      679       +1     
  Lines       18578    18753     +175     
  Branches     2270     2283      +13     
==========================================
+ Hits        16109    16271     +162     
- Misses       1726     1737      +11     
- Partials      743      745       +2     

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