fix: Admin Insights actual crash — function props across server/client boundary (v0.55.3)

Server logs (thanks to the user pulling them) showed the real error:
"Functions cannot be passed directly to Client Components" — the server
component page was passing formatShortDate/formatMonth as a `formatDate`
prop into TimeSeriesChart ("use client"). Functions aren't serializable
across the RSC boundary; the two previous fixes (query hardening,
Promise.allSettled) were real improvements but not the actual cause of
the reported crash.

TimeSeriesChart now takes a plain `dateFormat: "day" | "month"` string
and formats internally — BarChart was never affected (its formatValue
prop is only ever used via its own default, never passed from the page).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

apps/web/components/admin/charts/time-series-chart.tsx

@@ -5,22 +5,36 @@ import { cn } from "@/lib/utils";
 
 export type TimeSeriesPoint = { date: string; value: number };
 
+/** "day" expects "YYYY-MM-DD", "month" expects "YYYY-MM" — kept as a plain
+ *  string enum rather than a formatter function prop, since this chart is
+ *  a "use client" component and functions passed from a server component
+ *  parent aren't serializable across that boundary (React throws: "Functions
+ *  cannot be passed directly to Client Components"). */
+function formatPoint(date: string, kind: "day" | "month"): string {
+  if (kind === "month") {
+    const [y, m] = date.split("-");
+    return new Date(Number(y), Number(m) - 1, 1).toLocaleDateString(undefined, { month: "short", year: "2-digit" });
+  }
+  return new Date(`${date}T00:00:00Z`).toLocaleDateString(undefined, { month: "short", day: "numeric", timeZone: "UTC" });
+}
+
 /** Single-series area/line chart with a hover crosshair+tooltip and a
  *  table-view fallback — hand-rolled SVG, no charting lib. */
 export function TimeSeriesChart({
   data,
   formatValue = (n) => String(n),
-  formatDate = (d) => d,
+  dateFormat = "day",
   height = 200,
 }: {
   data: TimeSeriesPoint[];
   formatValue?: (n: number) => string;
-  formatDate?: (d: string) => string;
+  dateFormat?: "day" | "month";
   height?: number;
 }) {
   const [hovered, setHovered] = useState<number | null>(null);
   const [showTable, setShowTable] = useState(false);
   const svgRef = useRef<SVGSVGElement>(null);
+  const formatDate = (d: string) => formatPoint(d, dateFormat);
 
   const width = 600;
   const paddingBottom = 24;