feat(dashboard): lazy routes, Needs-you strip, URL state, exact numbers

- Workspace, SettingsHub, SessionDetail and the Workflow sub-tab are lazy
  (main bundle 2,166 kB -> ~920 kB), wrapped in RouteErrorBoundary: a stale
  chunk after a self-update reloads once (vite:preloadError too), any other
  error shows a Reload panel instead of a blank page.
- Live refresh: lib/throttle.ts + hooks/useLiveRefresh.ts replace trailing
  debounces that froze under a steady event stream; refresh skips hidden
  tabs and refetches after a WebSocket reconnect. Monitor loads only while
  shown, with one batched GET /api/agents?session_ids= instead of N+1; a
  failing endpoint is an inline error, not a blank Dashboard.
- NeedsYouStrip on Monitor and above Analytics. Tabs, filters, page, sort
  and search live in the URL (Dashboard, Sessions, Activity, SessionDetail).
- Sessions: tool / workspace / date-range filters, CSV/JSON export
  (formula-neutralised), focusable row links, Open in workspace (the dead
  /run links are gone), stale responses dropped, error + Retry.
- Fixes: "NaNs" durations, 30/7-day charts skipping idle days, weekday
  labels west of UTC (now averages), cache hit rate denominator, billable
  tokens vs cache reads, exact tool-call counts, "To" date = end of day,
  invalid ?from= no longer throws, recent list no longer shrinks to 15,
  stable message keys, transcript switch races.
- Light-theme-unreadable bg-black code panels and dark-only DAG fills use
  tokens; status configs and chart colours use theme tokens; Health tab
  and other literals translated.
- Server (additive): GET /api/agents?session_ids=, GET /api/sessions
  awaiting=1&from=&to=, stats tool_call_count/distinct_tool_count, event
  rows carry session/agent labels.

client/src/lib/__tests__/exportData.test.ts

@@ -0,0 +1,25 @@
+/**
+ * @file exportData.test.ts
+ * @description Unit tests for the CSV export helper: quoting and formula neutralizing.
+ * @author Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
+ */
+
+import { describe, it, expect } from "vitest";
+import { toCsv } from "../exportData";
+
+describe("toCsv", () => {
+  it("writes a header row and quotes cells that need it", () => {
+    const csv = toCsv(
+      [
+        { id: "a", name: 'say "hi", ok', n: 3 },
+        { id: "b", name: null, n: 0 },
+      ],
+      ["id", "name", "n"]
+    );
+    expect(csv).toBe('id,name,n\r\na,"say ""hi"", ok",3\r\nb,,0\r\n');
+  });
+
+  it("neutralizes spreadsheet formulas", () => {
+    expect(toCsv([{ v: "=HYPERLINK(1)" }], ["v"])).toBe("v\r\n'=HYPERLINK(1)\r\n");
+  });
+});

client/src/lib/__tests__/format.test.ts

@@ -17,6 +17,7 @@ import {
   formatTime,
   getCurrentLocale,
   formatModelName,
+  isoOrUndefined,
 } from "../format";
 
 describe("formatMs", () => {
@@ -256,3 +257,23 @@ describe("formatModelName", () => {
     expect(formatModelName("o1-preview")).toBe("O1 Preview");
   });
 });
+
+describe("NaN guards", () => {
+  it("formatDuration accepts timestamps that already end in Z", () => {
+    expect(formatDuration("2026-03-05T10:00:00Z", "2026-03-05T10:00:05Z")).toBe("5s");
+  });
+  it("formatMs renders '-' for NaN", () => {
+    expect(formatMs(NaN)).toBe("-");
+  });
+  it("timeAgo renders '-' for an unparseable timestamp", () => {
+    expect(timeAgo("not a date")).toBe("-");
+  });
+});
+
+describe("isoOrUndefined", () => {
+  it("returns undefined for an empty or unparseable value instead of throwing", () => {
+    expect(isoOrUndefined("")).toBeUndefined();
+    expect(isoOrUndefined("x")).toBeUndefined();
+    expect(isoOrUndefined("2026-01-02T03:04:05Z")).toBe("2026-01-02T03:04:05.000Z");
+  });
+});

client/src/lib/__tests__/throttle.test.ts

@@ -0,0 +1,41 @@
+/**
+ * @file throttle.test.ts
+ * @description Unit tests for the leading+trailing throttle used by live-refresh pages.
+ * @author Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
+ */
+
+import { describe, it, expect, vi, afterEach } from "vitest";
+import { throttle } from "../throttle";
+
+afterEach(() => vi.useRealTimers());
+
+describe("throttle", () => {
+  it("runs at once, then at most once per window with a trailing call", () => {
+    vi.useFakeTimers();
+    const fn = vi.fn();
+    const t = throttle(fn, 1000);
+    t();
+    expect(fn).toHaveBeenCalledTimes(1);
+    // A steady stream never freezes: it fires every window, not after it stops.
+    for (let i = 0; i < 25; i++) {
+      vi.advanceTimersByTime(100);
+      t();
+    }
+    expect(fn.mock.calls.length).toBeGreaterThanOrEqual(3);
+    vi.advanceTimersByTime(1000);
+    const n = fn.mock.calls.length;
+    vi.advanceTimersByTime(5000);
+    expect(fn).toHaveBeenCalledTimes(n);
+  });
+
+  it("cancel drops a pending trailing call", () => {
+    vi.useFakeTimers();
+    const fn = vi.fn();
+    const t = throttle(fn, 1000);
+    t();
+    t();
+    t.cancel();
+    vi.advanceTimersByTime(2000);
+    expect(fn).toHaveBeenCalledTimes(1);
+  });
+});