feat(01-02): create PageShell, StatCard, SummaryStrip, and DashboardSkeleton components

- PageShell: reusable page header with title, description, and action slot
- StatCard: KPI card with formatted value, semantic color, and optional variance badge
- SummaryStrip: responsive 3-card grid composing StatCards for income/expenses/balance
- DashboardSkeleton: pulse-animated loading placeholder mirroring real dashboard layout

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/components/dashboard/DashboardSkeleton.tsx

@@ -0,0 +1,49 @@
+import { Skeleton } from "@/components/ui/skeleton"
+import { Card, CardContent, CardHeader } from "@/components/ui/card"
+
+function SkeletonStatCard() {
+  return (
+    <Card>
+      <CardHeader className="pb-2">
+        <Skeleton className="h-4 w-24" />
+      </CardHeader>
+      <CardContent>
+        <Skeleton className="h-8 w-32" />
+        <Skeleton className="mt-1 h-3 w-20" />
+      </CardContent>
+    </Card>
+  )
+}
+
+export function DashboardSkeleton() {
+  return (
+    <div className="flex flex-col gap-6">
+      {/* Summary cards skeleton */}
+      <div className="grid gap-4 sm:grid-cols-2 lg:grid-cols-3">
+        <SkeletonStatCard />
+        <SkeletonStatCard />
+        <SkeletonStatCard />
+      </div>
+
+      {/* Chart area skeleton */}
+      <div className="grid gap-6 lg:grid-cols-2">
+        <Card>
+          <CardHeader>
+            <Skeleton className="h-5 w-40" />
+          </CardHeader>
+          <CardContent>
+            <Skeleton className="h-[240px] w-full rounded-md" />
+          </CardContent>
+        </Card>
+        <Card>
+          <CardHeader>
+            <Skeleton className="h-5 w-40" />
+          </CardHeader>
+          <CardContent>
+            <Skeleton className="h-[240px] w-full rounded-md" />
+          </CardContent>
+        </Card>
+      </div>
+    </div>
+  )
+}

src/components/dashboard/StatCard.tsx

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+import { TrendingUp, TrendingDown, Minus } from "lucide-react"
+
+import { cn } from "@/lib/utils"
+import { Card, CardContent, CardHeader, CardTitle } from "@/components/ui/card"
+
+interface StatCardProps {
+  title: string
+  value: string
+  valueClassName?: string
+  variance?: {
+    amount: string
+    direction: "up" | "down" | "neutral"
+    label: string
+  }
+}
+
+const directionIcon = {
+  up: TrendingUp,
+  down: TrendingDown,
+  neutral: Minus,
+} as const
+
+export function StatCard({
+  title,
+  value,
+  valueClassName,
+  variance,
+}: StatCardProps) {
+  return (
+    <Card>
+      <CardHeader className="pb-2">
+        <CardTitle className="text-sm font-medium text-muted-foreground">
+          {title}
+        </CardTitle>
+      </CardHeader>
+      <CardContent>
+        <p
+          className={cn(
+            "text-2xl font-bold tabular-nums tracking-tight",
+            valueClassName
+          )}
+        >
+          {value}
+        </p>
+        {variance && (
+          <div className="mt-1 flex items-center gap-1 text-xs text-muted-foreground">
+            {(() => {
+              const Icon = directionIcon[variance.direction]
+              return <Icon className="size-3" />
+            })()}
+            <span>{variance.amount}</span>
+            <span>{variance.label}</span>
+          </div>
+        )}
+      </CardContent>
+    </Card>
+  )
+}

src/components/dashboard/SummaryStrip.tsx

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+import { StatCard } from "./StatCard"
+
+interface SummaryStripProps {
+  income: { value: string; budgeted: string }
+  expenses: { value: string; budgeted: string }
+  balance: { value: string; isPositive: boolean }
+  t: (key: string) => string
+}
+
+export function SummaryStrip({
+  income,
+  expenses,
+  balance,
+  t,
+}: SummaryStripProps) {
+  return (
+    <div className="grid gap-4 sm:grid-cols-2 lg:grid-cols-3">
+      <StatCard
+        title={t("dashboard.totalIncome")}
+        value={income.value}
+        valueClassName="text-income"
+        variance={{
+          amount: income.budgeted,
+          direction: "neutral",
+          label: t("budgets.budgeted"),
+        }}
+      />
+      <StatCard
+        title={t("dashboard.totalExpenses")}
+        value={expenses.value}
+        valueClassName="text-destructive"
+        variance={{
+          amount: expenses.budgeted,
+          direction: "neutral",
+          label: t("budgets.budgeted"),
+        }}
+      />
+      <StatCard
+        title={t("dashboard.availableBalance")}
+        value={balance.value}
+        valueClassName={balance.isPositive ? "text-on-budget" : "text-over-budget"}
+      />
+    </div>
+  )
+}