fix(ui): wave 2 from critique re-run — AA contrast, unified PageHeader, checkout confirm

Nav: teams/settings/services back out of the nav until product-ready (user
decision); teams page was already half-finished (UUID member display is a
backend limitation).

Payment: explicit confirmation dialog (plan, amount, billing period, Stripe
note) before any redirect; ?plan= URL now pre-opens the dialog instead of
triggering a silent checkout.

Contrast AA sweep (71 replacements): functional micro-labels raised to
>=60-65% opacity and >=10px across sidebar, header, pricing, landing;
decorative all-caps 'interface' label removed.

Design unification: new PageHeader component (accent pill + serif
base/accent title) applied to settings, services, reviews, teams; pricing
header returned to the editorial voice (serif + accent pill); dead
GlossaryCard deleted.

i18n residuals: suggestion chips, 'Standard' provider label, notification
close, model-combobox strings extracted (+broken bg-surface/border-border-
subtle tokens fixed); ~45 new keys EN+FR; 13 dead keys removed; zero
missing keys verified.

Reviews: icon-only row actions now carry visible text; 'Approve all' is
two-step armed-confirm.

Accelerators: Ctrl/Cmd+Enter submits; arrow-key navigation in the language
combobox; recent-jobs history cap 8->20 with per-job download; source=target
config rejected; empty 'Master Quality' badge removed.

Cookie consent: reopenable via footer link, emoji replaced with drawn icon.

Verified: build exit 0, vitest 9/9, eslint 64 errors = previous level,
0 missing i18n keys.

frontend/src/app/dashboard/translate/LanguageSelector.tsx

@@ -70,16 +70,34 @@ function Combobox({
 
   const label = value === 'auto' ? autoLabel : allOptions.find(l => l.code === value)?.name ?? value;
 
+  const handleListboxKeys = (e: React.KeyboardEvent) => {
+    if (e.key === 'Escape' && open) {
+      e.stopPropagation();
+      closeAndRefocus();
+      return;
+    }
+    if (!open || (e.key !== 'ArrowDown' && e.key !== 'ArrowUp')) return;
+    e.preventDefault();
+    const options = Array.from(
+      ref.current?.querySelectorAll<HTMLButtonElement>('[role="option"]') ?? []
+    );
+    if (options.length === 0) return;
+    const idx = options.indexOf(document.activeElement as HTMLButtonElement);
+    const next = e.key === 'ArrowDown'
+      ? options[Math.min(options.length - 1, idx + 1)]
+      : options[Math.max(0, idx - 1)];
+    // from the search input, ArrowDown goes to the first option
+    (idx === -1 && document.activeElement === inputRef.current
+      ? options[e.key === 'ArrowDown' ? 0 : options.length - 1]
+      : next
+    ).focus();
+  };
+
   return (
     <div
       ref={ref}
       className="relative text-left"
-      onKeyDown={(e) => {
-        if (e.key === 'Escape' && open) {
-          e.stopPropagation();
-          closeAndRefocus();
-        }
-      }}
+      onKeyDown={handleListboxKeys}
     >
       <button
         ref={triggerRef}