[Client] add client conformance test suite (#279)

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/Conformance/conformance-baseline.yml

@@ -1,3 +1,28 @@
 server:
   - dns-rebinding-protection
 
+client:
+  - elicitation-sep1034-client-defaults
+  - sse-retry
+  - auth/metadata-default
+  - auth/metadata-var1
+  - auth/metadata-var2
+  - auth/metadata-var3
+  - auth/basic-cimd
+  - auth/scope-from-www-authenticate
+  - auth/scope-from-scopes-supported
+  - auth/scope-omitted-when-undefined
+  - auth/scope-step-up
+  - auth/scope-retry-limit
+  - auth/token-endpoint-auth-basic
+  - auth/token-endpoint-auth-post
+  - auth/token-endpoint-auth-none
+  - auth/pre-registration
+  - auth/2025-03-26-oauth-metadata-backcompat
+  - auth/2025-03-26-oauth-endpoint-fallback
+  - auth/offline-access-scope
+  - auth/offline-access-not-supported
+  - auth/client-credentials-jwt
+  - auth/client-credentials-basic
+  - auth/cross-app-access-complete-flow
+