feat(prefs): per-user UI font scale (A−/A+), saved to the profile

A header A−/value/A+ control scales the whole UI, persisted per user and
restored on login from any booth — cloning the theme-pref pattern end to end.

- DB: users.font_scale (migration 0014; percent, 100 = base, NOT NULL default).
- Server: PUT /api/auth/font-scale (auth-guarded; clamps to 80–160, snaps to a
  10-step); fontScale flows through sessionView → login + /me.
- Client: setFontScalePref + applyFontScale; applied in App alongside theme;
  FontScaleToggle in the header; i18n sq+en.

Scaling uses CSS `zoom` on the root, NOT root font-size: the app's type is pinned
in px (text-[12px] etc., ~230 spots), which a font-size change would not scale —
so the dense Active-sessions / Live-feed logs stayed tiny. `zoom` scales
everything uniformly (text, spacing, icons) like the browser's Ctrl+/−, which is
the readability win for operators who need larger text.

Tests: 4 font-scale auth-route cases (persist + /me, clamp/snap, 400, default-100).
Full workspace build/lint/test green.

Claude-Session: https://claude.ai/code/session_01Xcm6ikLgGoCxxHrxtjkk5V

apps/web/src/router.tsx

@@ -10,11 +10,23 @@ import { lazy, Suspense, useState } from "react";
 import { useTranslation } from "react-i18next";
 import { useQuery, useQueryClient } from "@tanstack/react-query";
 import type { Lang, Permission, SessionUser, Theme } from "./api.js";
-import { can, closeShift, fetchShiftReport, logout, openShift, setLanguagePref, setThemePref } from "./api.js";
+import {
+  can,
+  closeShift,
+  fetchShiftReport,
+  logout,
+  openShift,
+  setLanguagePref,
+  setThemePref,
+  setFontScalePref,
+  FONT_SCALE_MIN,
+  FONT_SCALE_MAX,
+  FONT_SCALE_STEP,
+} from "./api.js";
 import { qk, queryClient } from "./lib/query.js";
 import { Modal } from "./ui/Modal.js";
 import { setLanguage } from "./lib/i18n/index.js";
-import { applyTheme } from "./lib/theme.js";
+import { applyTheme, applyFontScale } from "./lib/theme.js";
 import { useLiveFeed } from "./lib/use-live-feed.js";
 import { useShift } from "./lib/use-shift.js";
 import { DeviceFooter } from "./ui/DeviceFooter.js";
@@ -210,6 +222,37 @@ function ThemeToggle({
   );
 }
 
+/** Header font-size control: A−/value/A+ scaling the whole UI (root font-size). Persisted
+ *  to the user profile like the theme, restored on next login. Local `active` state seeded
+ *  from the prop (the router context doesn't re-render on setUser); App's effect keeps the
+ *  DOM in sync with the persisted user on (re)login. */
+function FontScaleToggle({ user, setUser }: { user: SessionUser; setUser: (u: SessionUser | null) => void }) {
+  const { t } = useTranslation();
+  const [active, setActive] = useState<number>(user.fontScale);
+  function step(delta: number) {
+    const next = Math.min(FONT_SCALE_MAX, Math.max(FONT_SCALE_MIN, active + delta));
+    if (next === active) return;
+    setActive(next);
+    applyFontScale(next); // instant UI
+    setUser({ ...user, fontScale: next });
+    void setFontScalePref(next).catch(() => {
+      /* non-fatal — the choice still applies this session */
+    });
+  }
+  const btn = "rounded-term px-1.5 py-0.5 text-term-muted hover:text-term-text disabled:opacity-40";
+  return (
+    <div className="flex items-center gap-0.5 text-[10px] uppercase tracking-wider">
+      <button type="button" className={btn} onClick={() => step(-FONT_SCALE_STEP)} disabled={active <= FONT_SCALE_MIN} title={t("common.fontSmaller")} aria-label={t("common.fontSmaller")}>
+        A−
+      </button>
+      <span className="min-w-[2.5rem] text-center text-term-muted" title={t("common.fontSize")}>{active}%</span>
+      <button type="button" className={btn} onClick={() => step(FONT_SCALE_STEP)} disabled={active >= FONT_SCALE_MAX} title={t("common.fontLarger")} aria-label={t("common.fontLarger")}>
+        A+
+      </button>
+    </div>
+  );
+}
+
 /**
  * Header shift control — the site-wide single-open shift expressed as one button:
  *  - no shift open       → "Open shift" (enabled; opens this operator's shift)
@@ -399,6 +442,7 @@ function RootLayout() {
           {user && <ShiftButton />}
           {user && <LanguageToggle user={user} setUser={setUser} />}
           {user && <ThemeToggle user={user} setUser={setUser} />}
+          {user && <FontScaleToggle user={user} setUser={setUser} />}
           <StatusDot />
           {user && (
             <Link