feat(frontend): slice 2 — migrate 11 shared components to shadcn/Tailwind

Web UI rework. Shared-components slice (drift prevention):
- Migrate SectionCard, SelectionRailCard, TabbedCard, MetricCard,
  DiskSpaceCard, HoverEditButton, DialogFooter, ConfirmDialog,
  LibraryOverview, NowPlaying, SessionActivityPanel off @mui
- HoverEditButton: MUI IconButton + EditOutlined -> Button + lucide Pencil
- Status mapping uses the success Badge variant (chart-2) for healthy
- Exported APIs preserved so consuming pages still compile (no page edits)
- 11 behavioral Vitest component tests added

Gate: build + lint + test green.

frontend/src/components/ConfirmDialog.tsx

@@ -1,12 +1,17 @@
 import {
 	Dialog,
 	DialogContent,
+	DialogDescription,
+	DialogHeader,
 	DialogTitle,
-	Stack,
-	Typography,
-} from "@mui/material";
+} from "@/components/ui/dialog";
 import { DialogFooter } from "./DialogFooter";
 
+/**
+ * Reusable confirmation dialog built on the shadcn Dialog family and the
+ * shared `DialogFooter`. Same exported props as the MUI version; Esc / overlay
+ * click routes to `onCancel` via `onOpenChange`.
+ */
 export function ConfirmDialog({
 	open,
 	title,
@@ -25,23 +30,26 @@ export function ConfirmDialog({
 	busy?: boolean;
 }) {
 	return (
-		<Dialog open={open} onClose={onCancel} fullWidth maxWidth="xs">
-			<DialogTitle>{title}</DialogTitle>
-			<DialogContent>
-				<Stack spacing={1}>
-					<Typography variant="body2" color="text.secondary">
-						{message}
-					</Typography>
-				</Stack>
+		<Dialog
+			open={open}
+			onOpenChange={(next) => {
+				if (!next) onCancel();
+			}}
+		>
+			<DialogContent showCloseButton={false}>
+				<DialogHeader>
+					<DialogTitle>{title}</DialogTitle>
+					<DialogDescription>{message}</DialogDescription>
+				</DialogHeader>
+				<DialogFooter
+					onCancel={onCancel}
+					onConfirm={onConfirm}
+					confirmLabel={confirmLabel}
+					confirmColor="error"
+					confirmBusyLabel={confirmLabel}
+					confirmDisabled={busy}
+				/>
 			</DialogContent>
-			<DialogFooter
-				onCancel={onCancel}
-				onConfirm={onConfirm}
-				confirmLabel={confirmLabel}
-				confirmColor="error"
-				confirmBusyLabel={confirmLabel}
-				confirmDisabled={busy}
-			/>
 		</Dialog>
 	);
 }