Refactor AI Agent and AI Config handling across multiple files

- Updated function signatures to accept AI Agent and AI Config as non-pointer types for better clarity and safety.
- Modified instances where AI Agent and AI Config were dereferenced to improve code readability.
- Removed unnecessary nil checks for AI Agent and AI Config, simplifying the logic.
- Adjusted related tests and services to align with the new function signatures.
- Cleaned up code in runtime, skills, and executor packages to ensure consistency in handling AI configurations.

internal/ai/runtime/graphs/handoff_graph.go

@@ -33,10 +33,10 @@ func init() {
 
 type HandoffGraph struct {
 	conversation *models.Conversation
-	aiAgent      *models.AIAgent
+	aiAgent      models.AIAgent
 }
 
-func NewHandoffGraph(conversation *models.Conversation, aiAgent *models.AIAgent) *HandoffGraph {
+func NewHandoffGraph(conversation *models.Conversation, aiAgent models.AIAgent) *HandoffGraph {
 	return &HandoffGraph{
 		conversation: conversation,
 		aiAgent:      aiAgent,
@@ -44,7 +44,7 @@ func NewHandoffGraph(conversation *models.Conversation, aiAgent *models.AIAgent)
 }
 
 func (g *HandoffGraph) Run(ctx context.Context, argumentsInJSON string) (string, error) {
-	if g == nil || g.conversation == nil || g.aiAgent == nil {
+	if g == nil || g.conversation == nil {
 		return "", fmt.Errorf("handoff graph not initialized")
 	}
 	wasInterrupted, hasState, state := componenttool.GetInterruptState[HandoffGraphState](ctx)