fix(admin): restore LineChart component

LineChart is used by the dashboard page to render DAU trend charts.
It was accidentally removed during metrics cleanup — restore it.

admin/src/components/admin/LineChart.tsx

@@ -0,0 +1,169 @@
+"use client";
+
+import { format, parseISO } from "date-fns";
+
+interface DataPoint {
+  date: string;
+  value: number;
+}
+
+interface LineChartProps {
+  data: DataPoint[];
+  width?: number;
+  height?: number;
+  color?: string;
+  label: string;
+  unit?: string;
+}
+
+export default function LineChart({
+  data,
+  width = 600,
+  height = 200,
+  color = "#6366f1",
+  label,
+  unit = "",
+}: LineChartProps) {
+  if (data.length === 0) {
+    return (
+      <div style={{ color: "#737373", fontSize: "13px", textAlign: "center", padding: "32px" }}>
+        暂无数据
+      </div>
+    );
+  }
+
+  const padding = { top: 16, right: 16, bottom: 36, left: 44 };
+  const chartWidth = width - padding.left - padding.right;
+  const chartHeight = height - padding.top - padding.bottom;
+
+  const values = data.map((d) => d.value);
+  const maxValue = Math.max(...values, 1);
+  const minValue = 0;
+
+  function xScale(i: number) {
+    return padding.left + (i / (data.length - 1 || 1)) * chartWidth;
+  }
+
+  function yScale(v: number) {
+    return padding.top + chartHeight - ((v - minValue) / (maxValue - minValue || 1)) * chartHeight;
+  }
+
+  // Build SVG path
+  const pathD = data
+    .map((d, i) => `${i === 0 ? "M" : "L"} ${xScale(i).toFixed(1)} ${yScale(d.value).toFixed(1)}`)
+    .join(" ");
+
+  // Area path (fill under the line)
+  const areaD =
+    pathD +
+    ` L ${xScale(data.length - 1).toFixed(1)} ${(padding.top + chartHeight).toFixed(1)}` +
+    ` L ${padding.left} ${(padding.top + chartHeight).toFixed(1)} Z`;
+
+  // Y-axis ticks (5 ticks)
+  const yTicks = Array.from({ length: 5 }, (_, i) => {
+    const v = minValue + ((maxValue - minValue) * i) / 4;
+    return { v, y: yScale(v) };
+  });
+
+  // X-axis ticks (show every nth label based on data length)
+  const step = Math.max(1, Math.floor(data.length / 6));
+  const xTicks = data.filter((_, i) => i % step === 0 || i === data.length - 1);
+
+  const gradientId = `grad-${label.replace(/\s/g, "-")}`;
+
+  return (
+    <svg
+      width={width}
+      height={height}
+      style={{ display: "block", maxWidth: "100%" }}
+      aria-label={`${label} 趋势图`}
+    >
+      <defs>
+        <linearGradient id={gradientId} x1="0" y1="0" x2="0" y2="1">
+          <stop offset="0%" stopColor={color} stopOpacity={0.2} />
+          <stop offset="100%" stopColor={color} stopOpacity={0} />
+        </linearGradient>
+      </defs>
+
+      {/* Y-axis gridlines */}
+      {yTicks.map((t, i) => (
+        <line
+          key={i}
+          x1={padding.left}
+          y1={t.y}
+          x2={width - padding.right}
+          y2={t.y}
+          stroke="#e5e5e5"
+          strokeWidth={1}
+        />
+      ))}
+
+      {/* Y-axis labels */}
+      {yTicks.map((t, i) => (
+        <text
+          key={i}
+          x={padding.left - 6}
+          y={t.y + 4}
+          textAnchor="end"
+          fontSize={11}
+          fill="#737373"
+        >
+          {Math.round(t.v)}
+        </text>
+      ))}
+
+      {/* X-axis labels */}
+      {xTicks.map((d, i) => {
+        const idx = data.findIndex((x) => x.date === d.date);
+        return (
+          <text
+            key={i}
+            x={xScale(idx)}
+            y={padding.top + chartHeight + 16}
+            textAnchor="middle"
+            fontSize={11}
+            fill="#737373"
+          >
+            {(() => {
+              try {
+                return format(parseISO(d.date), "MM-dd");
+              } catch {
+                return d.date.slice(5);
+              }
+            })()}
+          </text>
+        );
+      })}
+
+      {/* Area fill */}
+      <path d={areaD} fill={`url(#${gradientId})`} />
+
+      {/* Line */}
+      <path d={pathD} fill="none" stroke={color} strokeWidth={2} strokeLinejoin="round" />
+
+      {/* Data points (dots) */}
+      {data.map((d, i) => (
+        <circle
+          key={i}
+          cx={xScale(i)}
+          cy={yScale(d.value)}
+          r={3}
+          fill={color}
+          stroke="white"
+          strokeWidth={1.5}
+          style={{ cursor: "default" }}
+        >
+          <title>
+            {(() => {
+              try {
+                return `${format(parseISO(d.date), "yyyy-MM-dd")}: ${d.value}${unit}`;
+              } catch {
+                return `${d.date}: ${d.value}${unit}`;
+              }
+            })()}
+          </title>
+        </circle>
+      ))}
+    </svg>
+  );
+}