feat(mcp) : add McpHeaderAuthenticator with rate limiting

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

config/packages/security.yaml

@@ -27,6 +27,12 @@ security:
             pattern: ^/api/session/profiles?$
             security: false
 
+        mcp:
+            pattern: ^/_mcp
+            stateless: true
+            custom_authenticators:
+                - App\Mcp\Security\McpHeaderAuthenticator
+
         api:
             pattern: ^/api
             stateless: false
@@ -49,6 +55,7 @@ security:
         - { path: ^/api/admin, roles: ROLE_ADMIN }
         - { path: ^/api/docs, roles: PUBLIC_ACCESS }
         - { path: ^/api/health$, roles: PUBLIC_ACCESS }
+        - { path: ^/_mcp, roles: ROLE_USER }
         - { path: ^/docs, roles: PUBLIC_ACCESS }
         - { path: ^/contexts, roles: PUBLIC_ACCESS }
         - { path: ^/\.well-known, roles: PUBLIC_ACCESS }