fix(logs): the browser's copy of a polled read is quiet too

The server now logs polled reads at DEBUG, and the browser's copy of each
request line promises the server's level: at INFO the unread-count polls
filled My log within minutes and, at Detailed, the shipped log. The server
marks a line it logged at DEBUG with X-Log-Quiet, so the polled-route list
stays in one place.

frontend/src/lib/http.test.ts

@@ -1,9 +1,10 @@
 import { afterEach, describe, expect, it, vi } from "vitest";
 
 import { pathTemplate, send } from "./http";
-import { clear, events } from "./log";
+import { clear, events, setLevel } from "./log";
 
 afterEach(() => {
+  setLevel("INFO");
   clear();
   vi.unstubAllGlobals();
 });
@@ -41,6 +42,18 @@ describe("send", () => {
     ]);
   });
 
+  // The server logs the reads the app polls at DEBUG and says so (`X-Log-Quiet`); at INFO the
+  // browser's copies filled My log with unread-count polls within minutes (prod UAT 2026-09-19).
+  it("logs a read the server called quiet at DEBUG, so the base level keeps it out", async () => {
+    vi.stubGlobal("fetch", async () => answer(200, { "X-Log-Quiet": "1" }));
+    await send("/api/messages/unread_count");
+    expect(events()).toEqual([]);
+
+    setLevel("DEBUG");
+    await send("/api/messages/unread_count");
+    expect(events().map((e) => e.level)).toEqual(["DEBUG"]);
+  });
+
   it("logs a network failure without the concrete path, and still rejects", async () => {
     vi.stubGlobal("fetch", async () => {
       throw new TypeError("Failed to fetch");