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/registry/registry_test.go

@@ -50,7 +50,7 @@ func TestResolveBuildsStaticToolMetadata(t *testing.T) {
 	})
 	toolSet, err := r.Resolve(registry.Context{
 		Conversation: &models.Conversation{ID: 1},
-		AIAgent:      &models.AIAgent{ID: 1},
+		AIAgent:      models.AIAgent{ID: 1},
 	})
 	if err != nil {
 		t.Fatalf("resolve returned error: %v", err)