feat(contact-button): add floating contact widget admin management

Add CMS support for floating contact widget with Facebook/Zalo quick
actions. Includes mongoose schema, admin UI tab, image upload with
sharp resize presets, deferred form submission with draft persistence,
and upload middleware error handling.

routes/admin.js

@@ -36,9 +36,34 @@ const videoGalleryController = require("../controllers/videoGalleryController");
 // Dashboard
 router.get("/dashboard", ensureAuthenticated, dashboardController.getDashboard);
 
+const runUploadMiddleware = (middleware) => (req, res, next) => {
+  middleware(req, res, (error) => {
+    if (!error) {
+      return next();
+    }
+
+    console.error("Upload middleware error:", error);
+
+    const status =
+      error.code === "LIMIT_FILE_SIZE"
+        ? 413
+        : error.statusCode || error.status || 400;
+
+    return res.status(status).json({
+      success: false,
+      error: error.message || "Upload failed",
+    });
+  });
+};
+
 // Home
 router.get("/home", ensureAuthenticated, homeController.index);
 router.post("/home/update", ensureAuthenticated, homeController.update);
+router.post(
+  "/home/floating-contact/update",
+  ensureAuthenticated,
+  homeController.updateFloatingContact,
+);
 router.get("/home/api/blogs", ensureAuthenticated, homeController.apiGetBlogs);
 
 // Middleware chuẩn hóa code
@@ -72,13 +97,13 @@ router.get("/upload", ensureAuthenticated, (req, res) => {
 router.post(
   "/upload/image",
   ensureAuthenticated,
-  upload.single("image"),
+  runUploadMiddleware(upload.single("image")),
   uploadController.uploadImage,
 );
 router.post(
   "/upload/video",
   ensureAuthenticated,
-  uploadVideo.single("video"),
+  runUploadMiddleware(uploadVideo.single("video")),
   uploadController.uploadVideo,
 );
 router.post(