Add export method dialog, extract shared Dialog primitive

Add export dialog with download/clipboard options and optional
undo/redo history inclusion (default off). Extract shared Dialog
component to ui/dialog.tsx, consolidating open/close lifecycle,
backdrop click, and escape key handling from all 6 dialog components.
Update spec to reflect export method dialog and optional history.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/web/src/components/ui/dialog.tsx

@@ -0,0 +1,50 @@
+import { type ReactNode, useEffect, useRef } from "react";
+import { cn } from "../../lib/utils.js";
+
+interface DialogProps {
+	open: boolean;
+	onClose: () => void;
+	className?: string;
+	children: ReactNode;
+}
+
+export function Dialog({ open, onClose, className, children }: DialogProps) {
+	const dialogRef = useRef<HTMLDialogElement>(null);
+
+	useEffect(() => {
+		const dialog = dialogRef.current;
+		if (!dialog) return;
+		if (open && !dialog.open) dialog.showModal();
+		else if (!open && dialog.open) dialog.close();
+	}, [open]);
+
+	useEffect(() => {
+		const dialog = dialogRef.current;
+		if (!dialog) return;
+		function handleCancel(e: Event) {
+			e.preventDefault();
+			onClose();
+		}
+		function handleBackdropClick(e: MouseEvent) {
+			if (e.target === dialog) onClose();
+		}
+		dialog.addEventListener("cancel", handleCancel);
+		dialog.addEventListener("mousedown", handleBackdropClick);
+		return () => {
+			dialog.removeEventListener("cancel", handleCancel);
+			dialog.removeEventListener("mousedown", handleBackdropClick);
+		};
+	}, [onClose]);
+
+	return (
+		<dialog
+			ref={dialogRef}
+			className={cn(
+				"m-auto rounded-lg border border-border bg-card text-foreground shadow-xl backdrop:bg-black/50",
+				className,
+			)}
+		>
+			<div className="p-6">{children}</div>
+		</dialog>
+	);
+}