feat(server): add brand kit management and project binding

Add a brand kit domain with memory and postgres stores, a BrandKitService
for CRUD and resolution, and REST endpoints to list, upsert, and delete
brand kits. Projects can bind a brand kit whose resolved context and
reference images feed into the agent's long-term memory and design prompts.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

server/internal/logic/query_project_logic.go

@@ -86,6 +86,7 @@ func toQueryProjectResponse(project design.Project, permission string, visibilit
 			Version:        project.Version,
 			SnapshotId:     nil,
 			ItemId:         nil,
+			BrandKitId:     project.BrandKitID,
 			Permission:     permission,
 		},
 	}