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/components/__tests__/RouteErrorBoundary.test.tsx

@@ -0,0 +1,60 @@
+/**
+ * @file RouteErrorBoundary.test.tsx
+ * @description The route error boundary: a failed lazy chunk (stale assets after
+ * a self-update) reloads the page once; any other error — or a second chunk
+ * failure — shows the themed Reload fallback instead of a blank app.
+ * @author Nguyễn Ngọc Trí Vĩ <vinnt@smartgift.vn>
+ */
+
+import { describe, it, expect, vi, beforeEach, afterEach } from "vitest";
+import { render, screen } from "@testing-library/react";
+import { RouteErrorBoundary, isChunkLoadError, reloadOnce } from "../RouteErrorBoundary";
+
+function Boom({ error }: { error: Error }): never {
+  throw error;
+}
+
+let reload: ReturnType<typeof vi.fn>;
+beforeEach(() => {
+  sessionStorage.clear();
+  reload = vi.fn();
+  vi.spyOn(console, "error").mockImplementation(() => {});
+});
+afterEach(() => vi.restoreAllMocks());
+
+describe("RouteErrorBoundary", () => {
+  it("recognises dynamic-import failures", () => {
+    expect(
+      isChunkLoadError(new TypeError("Failed to fetch dynamically imported module: /a.js"))
+    ).toBe(true);
+    expect(isChunkLoadError(Object.assign(new Error("x"), { name: "ChunkLoadError" }))).toBe(true);
+    expect(isChunkLoadError(new Error("Importing a module script failed."))).toBe(true);
+    expect(isChunkLoadError(new Error("boom"))).toBe(false);
+  });
+
+  it("reloads once on a chunk error, never twice in a row", () => {
+    expect(reloadOnce(reload)).toBe(true);
+    expect(reloadOnce(reload)).toBe(false);
+    expect(reload).toHaveBeenCalledTimes(1);
+  });
+
+  it("shows a Reload fallback for an ordinary render error", () => {
+    render(
+      <RouteErrorBoundary reload={reload}>
+        <Boom error={new Error("boom")} />
+      </RouteErrorBoundary>
+    );
+    expect(screen.getByRole("alert")).toHaveTextContent(/something went wrong/i);
+    expect(screen.getByRole("button", { name: /reload/i })).toBeInTheDocument();
+    expect(reload).not.toHaveBeenCalled();
+  });
+
+  it("reloads on a chunk error the first time", () => {
+    render(
+      <RouteErrorBoundary reload={reload}>
+        <Boom error={new TypeError("Failed to fetch dynamically imported module: /x.js")} />
+      </RouteErrorBoundary>
+    );
+    expect(reload).toHaveBeenCalledTimes(1);
+  });
+});