feat(03-01): add CSS animation tokens, i18n keys, and carryover display

- Add collapsible-open/close keyframes and CSS animation tokens to index.css
- Add dashboard.sections and dashboard.carryoverIncludes keys to en.json and de.json
- Add optional subtitle/subtitleClassName props to StatCard
- Extend SummaryStrip balance prop with carryoverSubtitle/carryoverIsNegative
- Compute and pass carryover subtitle from DashboardContent to SummaryStrip

src/components/dashboard/SummaryStrip.tsx

@@ -3,7 +3,12 @@ import { StatCard } from "./StatCard"
 interface SummaryStripProps {
   income: { value: string; budgeted: string }
   expenses: { value: string; budgeted: string }
-  balance: { value: string; isPositive: boolean }
+  balance: {
+    value: string
+    isPositive: boolean
+    carryoverSubtitle?: string
+    carryoverIsNegative?: boolean
+  }
   t: (key: string) => string
 }
 
@@ -39,6 +44,8 @@ export function SummaryStrip({
         title={t("dashboard.availableBalance")}
         value={balance.value}
         valueClassName={balance.isPositive ? "text-on-budget" : "text-over-budget"}
+        subtitle={balance.carryoverSubtitle}
+        subtitleClassName={balance.carryoverIsNegative ? "text-over-budget" : undefined}
       />
     </div>
   )