feat(02-02): create ExpenseDonutChart with center label and active hover

- Donut chart with innerRadius/outerRadius, center total label via formatCurrency
- Active sector expansion on hover via activeShape + Sector
- Custom legend below chart with color dots and formatted amounts
- CSS variable fills via ChartConfig (no hardcoded hex values)
- Empty state: ChartEmptyState placeholder when no data
- Zero-amount state: neutral muted ring with $0 center label
- ChartEmptyState shared component created (Rule 3: blocking dependency from Plan 01)

src/components/dashboard/charts/ChartEmptyState.tsx

@@ -0,0 +1,19 @@
+import { cn } from "@/lib/utils"
+
+interface ChartEmptyStateProps {
+  message: string
+  className?: string
+}
+
+export function ChartEmptyState({ message, className }: ChartEmptyStateProps) {
+  return (
+    <div
+      className={cn(
+        "flex min-h-[250px] w-full items-center justify-center rounded-lg border border-dashed border-muted-foreground/20 bg-muted/30",
+        className
+      )}
+    >
+      <p className="text-sm text-muted-foreground">{message}</p>
+    </div>
+  )
+}

src/components/dashboard/charts/ExpenseDonutChart.tsx

@@ -0,0 +1,156 @@
+import { useMemo, useState } from "react"
+import { PieChart, Pie, Cell, Sector, Label } from "recharts"
+import type { PieSectorDataItem } from "recharts/types/polar/Pie"
+import {
+  ChartContainer,
+  ChartTooltip,
+  ChartTooltipContent,
+} from "@/components/ui/chart"
+import type { ChartConfig } from "@/components/ui/chart"
+import { ChartEmptyState } from "./ChartEmptyState"
+import { formatCurrency } from "@/lib/format"
+
+interface ExpenseDonutChartProps {
+  data: Array<{ type: string; value: number; label: string }>
+  totalExpenses: number
+  currency: string
+  emptyMessage: string
+}
+
+function renderActiveShape(props: PieSectorDataItem) {
+  const { cx, cy, innerRadius, outerRadius, startAngle, endAngle, fill } =
+    props
+  return (
+    <Sector
+      cx={cx}
+      cy={cy}
+      innerRadius={innerRadius}
+      outerRadius={(outerRadius ?? 85) + 8}
+      startAngle={startAngle}
+      endAngle={endAngle}
+      fill={fill}
+    />
+  )
+}
+
+export function ExpenseDonutChart({
+  data,
+  totalExpenses,
+  currency,
+  emptyMessage,
+}: ExpenseDonutChartProps) {
+  const [activeIndex, setActiveIndex] = useState(-1)
+
+  const chartConfig = useMemo(() => {
+    const config: ChartConfig = {}
+    for (const entry of data) {
+      config[entry.type] = {
+        label: entry.label,
+        color: `var(--color-${entry.type}-fill)`,
+      }
+    }
+    return config
+  }, [data])
+
+  // No data at all: show empty state placeholder
+  if (data.length === 0 && totalExpenses === 0) {
+    return <ChartEmptyState message={emptyMessage} />
+  }
+
+  // Zero-amount state: budget exists but all actuals are zero
+  const isAllZero = totalExpenses === 0
+  const displayData = isAllZero
+    ? [{ type: "empty", value: 1, label: "" }]
+    : data
+  const displayConfig: ChartConfig = isAllZero
+    ? { empty: { label: "", color: "var(--color-muted)" } }
+    : chartConfig
+
+  return (
+    <div>
+      <ChartContainer config={displayConfig} className="min-h-[250px] w-full">
+        <PieChart>
+          <ChartTooltip
+            content={
+              <ChartTooltipContent
+                nameKey="type"
+                formatter={(value) =>
+                  formatCurrency(Number(value), currency)
+                }
+              />
+            }
+          />
+          <Pie
+            data={displayData}
+            dataKey="value"
+            nameKey="type"
+            innerRadius={60}
+            outerRadius={85}
+            cx="50%"
+            cy="50%"
+            activeIndex={isAllZero ? undefined : activeIndex}
+            activeShape={isAllZero ? undefined : renderActiveShape}
+            onMouseEnter={
+              isAllZero ? undefined : (_, index) => setActiveIndex(index)
+            }
+            onMouseLeave={
+              isAllZero ? undefined : () => setActiveIndex(-1)
+            }
+          >
+            {displayData.map((entry) => (
+              <Cell
+                key={entry.type}
+                fill={
+                  isAllZero
+                    ? "var(--color-muted)"
+                    : `var(--color-${entry.type}-fill)`
+                }
+              />
+            ))}
+            <Label
+              content={({ viewBox }) => {
+                if (viewBox && "cx" in viewBox && "cy" in viewBox) {
+                  return (
+                    <text
+                      x={viewBox.cx}
+                      y={viewBox.cy}
+                      textAnchor="middle"
+                      dominantBaseline="middle"
+                    >
+                      <tspan className="fill-foreground text-xl font-bold">
+                        {formatCurrency(totalExpenses, currency)}
+                      </tspan>
+                    </text>
+                  )
+                }
+              }}
+            />
+          </Pie>
+        </PieChart>
+      </ChartContainer>
+
+      {/* Custom legend below the donut */}
+      {!isAllZero && data.length > 0 && (
+        <ul className="mt-2 space-y-1">
+          {data.map((entry) => (
+            <li
+              key={entry.type}
+              className="flex items-center gap-2 text-sm"
+            >
+              <span
+                className="inline-block size-3 shrink-0 rounded-full"
+                style={{
+                  backgroundColor: `var(--color-${entry.type}-fill)`,
+                }}
+              />
+              <span className="text-muted-foreground">{entry.label}</span>
+              <span className="ml-auto font-medium tabular-nums">
+                {formatCurrency(entry.value, currency)}
+              </span>
+            </li>
+          ))}
+        </ul>
+      )}
+    </div>
+  )
+}