Relation reads batched and unnested #206

Task #204 completed the remaining database-read cleanup identified during #119. Relation listing now batches endpoint, task-title, and visibility-filtered memory-title reads without holding one DbContext while authorization services open another.

Commit dabb48f was deployed. ProjectItemService.Resolve and KnowledgeService.GetProjectMemory now dispose lookup contexts before delegated reads. Relation visibility remains intact for private, public, archived, expired, unpublished, and task-only targets. Focused tests passed 4/4.