fix: make draw.io built-in save button work with mouse tracking (#296)

- Add showSaveDialog state to DiagramContext for shared state
- Add mouse tracking to only respond to save events when mouse is over draw.io panel
- Prevents save dialog from opening when clicking Send in chat panel
- Add DialogDescription to SaveDialog for accessibility

components/chat-input.tsx

@@ -155,12 +155,16 @@ export function ChatInput({
     minimalStyle = false,
     onMinimalStyleChange = () => {},
 }: ChatInputProps) {
-    const { diagramHistory, saveDiagramToFile } = useDiagram()
+    const {
+        diagramHistory,
+        saveDiagramToFile,
+        showSaveDialog,
+        setShowSaveDialog,
+    } = useDiagram()
     const textareaRef = useRef<HTMLTextAreaElement>(null)
     const fileInputRef = useRef<HTMLInputElement>(null)
     const [isDragging, setIsDragging] = useState(false)
     const [showClearDialog, setShowClearDialog] = useState(false)
-    const [showSaveDialog, setShowSaveDialog] = useState(false)
 
     // Allow retry when there's an error (even if status is still "streaming" or "submitted")
     const isDisabled =