Add integration tests for CIMD embedded auth server support

[amirejaz]

Summary

• Stacked on Wire CIMD config through embedded AS and enable storage decorator #5348 (wire CIMD config through embedded AS). Merge that first.
• Adds four integration tests in test/integration/authserver/ that exercise the CIMD feature end-to-end against a real EmbeddedAuthServer instance — no mocks, no binary required:
  1. Discovery — client_id_metadata_document_supported: true appears in both /.well-known/oauth-authorization-server and /.well-known/openid-configuration when CIMD is enabled; absent when disabled
  2. Authorize accepts CIMD URL — /oauth/authorize with a CIMD URL as client_id redirects to the upstream IDP without prior DCR registration
  3. Authorize rejects CIMD URL when disabled — same request fails when CIMD is off
  4. No DCR required — flow completes without any call to /oauth/register, proving on-the-fly client resolution works

Also adds WithCIMD functional option to the integration test helper in test/integration/authserver/helpers/authserver.go.

Type of change

• Test coverage (no production code change)

Test plan

• go test ./test/integration/authserver/... passes
• task lint-fix clean

Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 68.80%. Comparing base (1d2c18c) to head (d27bbf5).

Additional details and impacted files

@@                    Coverage Diff                     @@
##           cimd-phase2-pr3-wiring    #5379      +/-   ##
==========================================================
+ Coverage                   68.77%   68.80%   +0.03%     
==========================================================
  Files                         627      627              
  Lines                       63625    63629       +4     
==========================================================
+ Hits                        43759    43783      +24     
+ Misses                      16612    16593      -19     
+ Partials                     3254     3253       -1     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.