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_test.go

@@ -1,41 +0,0 @@
-package graphs
-
-import (
-	"testing"
-
-	"cs-agent/internal/models"
-)
-
-func TestHandoffGraphBuildReason(t *testing.T) {
-	graph := NewHandoffGraph(&models.Conversation{ID: 1}, &models.AIAgent{Name: "AI"})
-
-	reason, err := graph.buildReason(`{"reason":"  用户需要人工确认  "}`)
-	if err != nil {
-		t.Fatalf("buildReason returned error: %v", err)
-	}
-	if reason != "用户需要人工确认" {
-		t.Fatalf("unexpected reason: %q", reason)
-	}
-}
-
-func TestHandoffGraphBuildReasonFallback(t *testing.T) {
-	graph := NewHandoffGraph(&models.Conversation{ID: 1}, &models.AIAgent{Name: "AI"})
-
-	reason, err := graph.buildReason(`{}`)
-	if err != nil {
-		t.Fatalf("buildReason returned error: %v", err)
-	}
-	if reason != "用户需要转人工支持" {
-		t.Fatalf("unexpected fallback reason: %q", reason)
-	}
-}
-
-func TestHandoffGraphBuildSuccessReply(t *testing.T) {
-	graph := NewHandoffGraph(&models.Conversation{ID: 1}, &models.AIAgent{Name: "AI"})
-
-	got := graph.buildSuccessReply()
-	want := "已为你转接人工客服，请稍候。，请稍候。"
-	if got != want {
-		t.Fatalf("unexpected success reply: %q", got)
-	}
-}