refactor(monitoring): remove orphaned frontend DiskSpaceCard (slice 2)

After slice 1 removed /api/monitoring/disk, the frontend DiskSpaceCard
component (and its DiskSpace type) had zero importers — it fed nothing.
Delete them.

Removed (frontend):
- components/DiskSpaceCard.tsx
- components/__tests__/DiskSpaceCard.test.tsx
- types/index.ts: DiskSpace interface

Gate: build + lint + vitest (22 files / 63 tests) green.

frontend/src/components/DiskSpaceCard.tsx

@@ -1,78 +0,0 @@
-import { Card, CardContent } from "@/components/ui/card";
-import { Progress } from "@/components/ui/progress";
-
-interface Props {
-	used: number;
-	available: number;
-	size: number;
-	usedPct: string;
-}
-
-function formatBytes(bytes: number): string {
-	if (!bytes || bytes === 0) return "0 B";
-	const units = ["B", "KB", "MB", "GB", "TB"];
-	let value = bytes;
-	let unitIdx = 0;
-	while (value >= 1000 && unitIdx < units.length - 1) {
-		value /= 1000;
-		unitIdx++;
-	}
-	return `${value.toFixed(1)} ${units[unitIdx]}`;
-}
-
-/**
- * Progress-bar class (full static strings so Tailwind's scanner emits them).
- * `chart-2`=success, `chart-3`=warning, `destructive`=error, per design §2.3.
- */
-function progressBarClass(pct: number): string {
-	if (pct < 70) {
-		return "h-3 [&_[data-slot=progress-indicator]]:bg-chart-2";
-	}
-	if (pct < 90) {
-		return "h-3 [&_[data-slot=progress-indicator]]:bg-chart-3";
-	}
-	return "h-3 [&_[data-slot=progress-indicator]]:bg-destructive";
-}
-
-/**
- * Dashboard card that summarizes the configured media disk.
- *
- * Keeps the progress bar inside the card so the capacity signal, raw byte
- * values, and free-space breakdown stay visually grouped. The used / free /
- * total / percent breakdown is preserved verbatim from the MUI version.
- */
-export function DiskSpaceCard({ used, available, size, usedPct }: Props) {
-	const pct = Math.max(0, Math.min(100, Number.parseFloat(usedPct) || 0));
-	const cells = [
-		{ label: "Used", value: formatBytes(used) },
-		{ label: "Free", value: formatBytes(available) },
-		{ label: "Total", value: formatBytes(size) },
-	];
-
-	return (
-		<Card className="h-full">
-			<CardContent className="flex flex-col gap-4">
-				<div className="flex flex-col gap-1">
-					<span className="text-sm uppercase tracking-wide text-muted-foreground">
-						Disk space
-					</span>
-					<span className="text-lg font-semibold">{usedPct} used</span>
-				</div>
-				<Progress value={pct} className={progressBarClass(pct)} />
-				<div className="grid grid-cols-1 gap-4 sm:grid-cols-3">
-					{cells.map((cell) => (
-						<div
-							key={cell.label}
-							className="flex h-full flex-col items-center justify-center gap-1 rounded-lg bg-muted/50 p-3 text-center"
-						>
-							<span className="text-xs text-muted-foreground">
-								{cell.label}
-							</span>
-							<span className="text-sm font-semibold">{cell.value}</span>
-						</div>
-					))}
-				</div>
-			</CardContent>
-		</Card>
-	);
-}

frontend/src/components/__tests__/DiskSpaceCard.test.tsx

@@ -1,22 +0,0 @@
-import { describe, it, expect } from "vitest";
-import { render, screen } from "@testing-library/react";
-import { DiskSpaceCard } from "../DiskSpaceCard";
-
-describe("DiskSpaceCard", () => {
-	it("preserves the used / free / total breakdown and percent headline", () => {
-		render(
-			<DiskSpaceCard
-				used={500000000000}
-				available={500000000000}
-				size={1000000000000}
-				usedPct="50"
-			/>,
-		);
-		expect(screen.getByText(/50 used/i)).toBeInTheDocument();
-		expect(screen.getByText("Used")).toBeInTheDocument();
-		expect(screen.getByText("Free")).toBeInTheDocument();
-		expect(screen.getByText("Total")).toBeInTheDocument();
-		// Disk space label
-		expect(screen.getByText(/disk space/i)).toBeInTheDocument();
-	});
-});