Add read-only workflow template catalog API

[AbigailDeng]

Summary

• Add strong typed workflow template summary, detail, requirements, compatibility, paging, and lookup contracts behind a narrow Application query port.
• Add an immutable embedded Infrastructure catalog that accepts only code registrations, validates returned YAML with the canonical workflow parser, and supports search, category filters, stable cursors, exact revisions, and explicit disabled or incompatible results.
• Add authenticated Studio list and revision-detail endpoints with ETag, conditional requests, immutable detail caching, bounded inputs, safe logging, and focused coverage.

Verification

• dotnet build src/Aevatar.Studio.Hosting/Aevatar.Studio.Hosting.csproj --nologo --no-restore: passed
• dotnet test test/Aevatar.Studio.Tests/Aevatar.Studio.Tests.csproj --nologo --no-restore --filter FullyQualifiedName~EmbeddedWorkflowTemplateCatalogQueryPortTests|FullyQualifiedName~WorkflowTemplateEndpointsTests|FullyQualifiedName~StudioInfrastructureServiceCollectionExtensionsTests: passed (15 tests)
• bash tools/ci/test_stability_guards.sh: passed
• bash tools/ci/query_projection_priming_guard.sh: passed
• bash tools/ci/architecture_guards.sh: passed
• bash tools/docs/lint.sh: passed

Risks

• None identified. V1 intentionally registers no concrete templates per issue scope.

Closes #2967

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.45%. Comparing base (5426eff) to head (17cf2e7).

@@           Coverage Diff           @@
##              dev    #2973   +/-   ##
=======================================
  Coverage   83.45%   83.45%           
=======================================
  Files        1376     1376           
  Lines      112732   112732           
  Branches    14366    14366           
=======================================
+ Hits        94084    94085    +1     
+ Misses      12096    12094    -2     
- Partials     6552     6553    +1     

Flag	Coverage Δ
ci	83.45% <ø> (+<0.01%)	⬆️

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