⚡️ perf(webview): 降低首屏加载与 WebView2 内存占用

- Monaco Editor 改为首次使用时按需初始化
- AI 面板改为懒加载，延后加载 Markdown 和图表渲染依赖
- 增加 Windows 低内存视觉模式，支持关闭透明 WebView 和 Acrylic
- 补充低内存启动说明与模式解析测试

main_test.go

@@ -0,0 +1,26 @@
+package main
+
+import "testing"
+
+func TestIsLowMemoryMode(t *testing.T) {
+	tests := []struct {
+		name string
+		env  string
+		want bool
+	}{
+		{name: "disabled by default", env: "", want: false},
+		{name: "enabled with one", env: "1", want: true},
+		{name: "enabled with true", env: "true", want: true},
+		{name: "enabled with yes and whitespace", env: " yes ", want: true},
+		{name: "disabled with false", env: "false", want: false},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Setenv("GONAVI_LOW_MEMORY_MODE", tt.env)
+			if got := isLowMemoryMode(); got != tt.want {
+				t.Fatalf("isLowMemoryMode() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}