refactor: change pointer receivers to value types for Conversation and UserMessage in various structs and functions

internal/ai/runtime/registry/registry_test.go

@@ -49,7 +49,7 @@ func TestResolveBuildsStaticToolMetadata(t *testing.T) {
 		code: toolx.GraphCreateTicketConfirm.Code,
 	})
 	toolSet, err := r.Resolve(registry.Context{
-		Conversation: &models.Conversation{ID: 1},
+		Conversation: models.Conversation{ID: 1},
 		AIAgent:      models.AIAgent{ID: 1},
 	})
 	if err != nil {

internal/ai/runtime/registry/types.go

@@ -9,10 +9,10 @@ import (
 )
 
 type Context struct {
-	Conversation     *models.Conversation
+	Conversation     models.Conversation
 	AIAgent          models.AIAgent
 	AIConfig         models.AIConfig
-	UserMessage      *models.Message
+	UserMessage      models.Message
 	AllowedToolCodes []string
 }