Establishes shared infrastructure for content services:
- Common dependencies (DocumentRepository, AuditService, UserIdKeyResolver)
- Audit helper methods (sync and async)
- Inherits from RepositoryService for scope/query support
- Adds ContentServiceConstants for shared constants (batch page size)
Updated tracking test to look for correct assembly location.
Tracking test now fails (expected) - signals class exists for future work.
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Co-Authored-By: Claude <noreply@anthropic.com>
