feat(frontend): wire Vite app to FastAPI parser with NDJSON streaming + Upload page

src/lib/format.ts

@@ -0,0 +1,66 @@
+const usd = new Intl.NumberFormat("en-US", {
+  style: "currency",
+  currency: "USD",
+  maximumFractionDigits: 0,
+});
+
+const usdPrecise = new Intl.NumberFormat("en-US", {
+  style: "currency",
+  currency: "USD",
+  minimumFractionDigits: 2,
+  maximumFractionDigits: 2,
+});
+
+const number = new Intl.NumberFormat("en-US");
+
+const date = new Intl.DateTimeFormat("en-US", {
+  month: "short",
+  day: "numeric",
+  year: "numeric",
+});
+
+const dateShort = new Intl.DateTimeFormat("en-US", {
+  month: "short",
+  day: "numeric",
+});
+
+const time = new Intl.DateTimeFormat("en-US", {
+  hour: "numeric",
+  minute: "2-digit",
+});
+
+const relative = new Intl.RelativeTimeFormat("en-US", { numeric: "auto" });
+
+/**
+ * Coerce a backend Decimal-serialized value (string) or a number to a finite
+ * number. Returns the supplied fallback (default 0) on null/undefined/NaN.
+ * Used everywhere the FastAPI `Decimal` field needs to flow into a UI that
+ * expects `number`.
+ */
+export const toNum = (v: string | number | null | undefined, fallback = 0): number => {
+  if (v === null || v === undefined) return fallback;
+  const n = typeof v === "number" ? v : Number(v);
+  return Number.isFinite(n) ? n : fallback;
+};
+
+export const fmt = {
+  usd: (n: number) => usd.format(n),
+  usdPrecise: (n: number) => usdPrecise.format(n),
+  usdDecimal: (v: string | number | null | undefined) =>
+    usdPrecise.format(toNum(v)),
+  num: (n: number) => number.format(n),
+  date: (iso: string) => date.format(new Date(iso)),
+  dateShort: (iso: string) => dateShort.format(new Date(iso)),
+  time: (iso: string) => time.format(new Date(iso)),
+  pct: (n: number, digits = 1) => `${n.toFixed(digits)}%`,
+  relative: (iso: string) => {
+    const ms = new Date(iso).getTime() - Date.now();
+    const minutes = Math.round(ms / 60_000);
+    if (Math.abs(minutes) < 60) return relative.format(minutes, "minute");
+    const hours = Math.round(minutes / 60);
+    if (Math.abs(hours) < 24) return relative.format(hours, "hour");
+    const days = Math.round(hours / 24);
+    if (Math.abs(days) < 7) return relative.format(days, "day");
+    return fmt.date(iso);
+  },
+};