feat: delete photo from server on remove + fix file drag-and-drop

- DELETE /api/upload?url= endpoint removes file from disk (with path traversal protection)
- api.upload.deletePhoto() helper in frontend
- removePhoto() now calls deletePhoto for cdn.hotelsync.ru URLs (best-effort)
- handleDragOver only highlights drop zone for external file drags (not thumbnail DnD)
- <img> in preview gets draggable={false} + pointer-events-none to not interfere with drops

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/pages/RoomCategoriesPage.tsx

@@ -81,12 +81,28 @@ function CategoryForm({ category, onClose, onSave }: CategoryFormProps) {
   const handleDrop = (e: React.DragEvent) => {
     e.preventDefault()
     setDragging(false)
-    uploadFiles(e.dataTransfer.files)
+    // Only handle external file drops (not internal thumbnail DnD)
+    if (e.dataTransfer.files.length > 0) {
+      uploadFiles(e.dataTransfer.files)
+    }
+  }
+
+  const handleDragOver = (e: React.DragEvent) => {
+    e.preventDefault()
+    // Only show drop highlight for external files, not internal thumbnail reorder
+    if (e.dataTransfer.types.includes('Files')) {
+      setDragging(true)
+    }
   }
 
   const removePhoto = (i: number) => {
+    const url = photos[i]
     setPhotos(prev => prev.filter((_, idx) => idx !== i))
     setPhotoIdx(p => Math.max(0, p - 1))
+    // Delete from server (best-effort, don't block UI)
+    if (url.startsWith('https://cdn.hotelsync.ru/')) {
+      api.upload.deletePhoto(url).catch(console.error)
+    }
   }
 
   const handleSave = async () => {
@@ -224,11 +240,11 @@ function CategoryForm({ category, onClose, onSave }: CategoryFormProps) {
                       dragging && 'ring-2 ring-brand-500 ring-offset-2',
                     )}
                     style={{ height: 220 }}
-                    onDragOver={e => { e.preventDefault(); setDragging(true) }}
+                    onDragOver={handleDragOver}
                     onDragLeave={() => setDragging(false)}
                     onDrop={handleDrop}
                   >
-                    <img src={photos[photoIdx]} alt="" className="w-full h-full object-cover" />
+                    <img src={photos[photoIdx]} alt="" draggable={false} className="w-full h-full object-cover pointer-events-none" />
                     {dragging && (
                       <div className="absolute inset-0 bg-brand-600/40 flex items-center justify-center">
                         <p className="text-white font-semibold text-sm">Отпустите для добавления</p>
@@ -290,7 +306,7 @@ function CategoryForm({ category, onClose, onSave }: CategoryFormProps) {
                       : 'border-slate-300 dark:border-slate-600 text-slate-400 hover:border-slate-400',
                   )}
                   onClick={() => fileRef.current?.click()}
-                  onDragOver={e => { e.preventDefault(); setDragging(true) }}
+                  onDragOver={handleDragOver}
                   onDragLeave={() => setDragging(false)}
                   onDrop={handleDrop}
                 >