ApiKeyAuthenticator, PermissionVoter and UserProvider implement
Symfony Security for the API (Bearer token) and admin (session) flows.
Domain repository interfaces added for ApiKey, User, AIPipelineJob and
Invoice; Doctrine implementations provided.
Also adds DatabaseLogHandler for structured DB logging, SerpApiWebSearch,
and the LogEntry domain entity.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>