新增单元测试验证图片重定向逻辑，优化前端预览链接样式，调整依赖配置

internal/http/handlers/image_test.go

@@ -0,0 +1,68 @@
+package handlers
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"BingPaper/internal/config"
+	"BingPaper/internal/model"
+	"github.com/gin-gonic/gin"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestHandleImageResponseRedirect(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+
+	// Setup config
+	err := config.Init("")
+	assert.NoError(t, err)
+	config.GetConfig().API.Mode = "redirect"
+
+	// Mock Image and Variant
+	img := &model.Image{
+		Date:    "2026-01-26",
+		URLBase: "/th?id=OHR.TestImage",
+		Variants: []model.ImageVariant{
+			{
+				Variant:    "UHD",
+				Format:     "jpg",
+				PublicURL:  "", // Empty for local storage simulation
+				StorageKey: "2026-01-26/2026-01-26_UHD.jpg",
+			},
+		},
+	}
+
+	t.Run("Redirect mode with empty PublicURL should redirect to Bing", func(t *testing.T) {
+		w := httptest.NewRecorder()
+		c, _ := gin.CreateTestContext(w)
+		c.Request, _ = http.NewRequest("GET", "/api/v1/image/today?variant=UHD", nil)
+
+		handleImageResponse(c, img)
+
+		assert.Equal(t, http.StatusFound, w.Code)
+		assert.Contains(t, w.Header().Get("Location"), "bing.com")
+		assert.Contains(t, w.Header().Get("Location"), "UHD")
+	})
+
+	t.Run("FormatMeta in redirect mode should return Bing URL if PublicURL is empty", func(t *testing.T) {
+		config.GetConfig().API.Mode = "redirect"
+		meta := formatMeta(img)
+
+		variants := meta["variants"].([]gin.H)
+		assert.Equal(t, 1, len(variants))
+		assert.Contains(t, variants[0]["url"].(string), "bing.com")
+		assert.Contains(t, variants[0]["url"].(string), "UHD")
+	})
+
+	t.Run("FormatMeta in local mode should return API URL", func(t *testing.T) {
+		config.GetConfig().API.Mode = "local"
+		config.GetConfig().Server.BaseURL = "http://myserver.com"
+		meta := formatMeta(img)
+
+		variants := meta["variants"].([]gin.H)
+		assert.Equal(t, 1, len(variants))
+		assert.Contains(t, variants[0]["url"].(string), "myserver.com")
+		assert.Contains(t, variants[0]["url"].(string), "/api/v1/image/date/")
+	})
+}