feat: add drag and drop support to Upload Style area (#1852)

## Feat: Add drag and drop support to Upload Style area

Closes #911

---

### Problem
The Upload Style area only supported click-to-upload. Users could not
drag and drop a JSON file directly onto it.

### Fix
Added `onDragOver` and `onDrop` event handlers to the Upload Style area.
The dropped file is passed to the existing file reading logic already
used by the Upload button. A visual highlight is shown when dragging
over the area.

src/locales/de/translation.json

@@ -199,5 +199,6 @@
   "Video URL": "Video-URL",
   "View": "Ansicht",
   "You've entered an old style filter.": "Du hast einen alten Filter-Stil eingegeben.",
-  "Zoom": "Zoom"
+  "Zoom": "Zoom",
+  "Drag and drop a style JSON file here or click to browse": "Ziehen Sie eine Style-JSON-Datei hierher oder klicken Sie, um zu durchsuchen"
 }

src/locales/en/translation.json

@@ -0,0 +1,3 @@
+{
+  "Drag and drop a style JSON file here or click to browse": "Drag and drop a style JSON file here or click to browse"
+}

src/locales/fr/translation.json

@@ -199,5 +199,6 @@
   "Video URL": "URL de la vidéo",
   "View": "Vue",
   "You've entered an old style filter.": "Vous avez entré un ancien style de filtre.",
-  "Zoom": "Zoom"
+  "Zoom": "Zoom",
+  "Drag and drop a style JSON file here or click to browse": "Faites glisser un fichier JSON de style ici ou cliquez pour parcourir"
 }

src/locales/he/translation.json

@@ -199,5 +199,6 @@
   "Video URL": "כתובת וידאו",
   "View": "תצוגה",
   "You've entered an old style filter.": "הכנסתם סינון מסוג ישן,",
-  "Zoom": "זום"
+  "Zoom": "זום",
+  "Drag and drop a style JSON file here or click to browse": "גרור ושחרר כאן קובץ JSON של סגנון או לחץ כדי לעיין"
 }

src/locales/it/translation.json

@@ -199,5 +199,6 @@
   "Video URL": "Indirizzo video",
   "View": "Vista",
   "You've entered an old style filter.": "Hai inserito uno stile filtro obsoleto.",
-  "Zoom": "Zoom"
+  "Zoom": "Zoom",
+  "Drag and drop a style JSON file here or click to browse": "Trascina e rilascia qui un file JSON dello stile o fai clic per sfogliare"
 }

src/locales/ja/translation.json

@@ -199,5 +199,6 @@
   "Video URL": "動画URL",
   "View": "表示",
   "You've entered an old style filter.": "旧型フィルタを使用しております。",
-  "Zoom": "ズーム"
+  "Zoom": "ズーム",
+  "Drag and drop a style JSON file here or click to browse": "ここにスタイルのJSONファイルをドラッグ＆ドロップするか、クリックして参照してください"
 }

src/locales/ko/translation.json

@@ -199,5 +199,6 @@
   "Video URL": "비디오 URL",
   "View": "보기",
   "You've entered an old style filter.": "이전 스타일 필터를 입력했습니다.",
-  "Zoom": "줌"
+  "Zoom": "줌",
+  "Drag and drop a style JSON file here or click to browse": "여기에 스타일 JSON 파일을 끌어다 놓거나 클릭하여 찾아보세요"
 }

src/locales/zh/translation.json

@@ -199,5 +199,6 @@
   "Video URL": "视频URL",
   "View": "视图",
   "You've entered an old style filter.": "您输入了一个旧风格的过滤器。",
-  "Zoom": "缩放"
+  "Zoom": "缩放",
+  "Drag and drop a style JSON file here or click to browse": "将样式 JSON 文件拖放到此处或点击以浏览"
 }