#276 CONV-315: Document API authentication

Summary

• Adds test asserting Bearer API key authentication scheme is documented in OpenAPI spec
• Auth scheme was already in the skeleton; test formalizes the contract

Test plan

• composer test passes (604 tests)

🤖 Generated with Claude Code

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Summary by cubic

Add a test that verifies the OpenAPI spec declares Bearer token auth via components.securitySchemes.ApiKeyBearer (type http, scheme bearer). This satisfies CONV-315’s requirement to document API authentication and guards against regressions.