refactor(gamification): collapse achievement consumers onto shared hook

v1.4.34 IW-F-Perf — migrate `<RecentAchievementsCard>`, the
`/achievements` mother page, and `<AchievementUnlockNotifier>` from
ad-hoc `useQuery` blocks onto `useAchievementsQuery()`.

Pre-change the dashboard cold mount fired
`/api/gamification/achievements` twice — once for the card, once for
the notifier — because the notifier carried a per-user discriminator
on its queryKey and TanStack treated it as a fresh cache cell. The
shared hook routes all three consumers through the same
`queryKeys.gamificationAchievements()` slot, so a single network
call now backs every surface. The notifier keeps its 2-minute
refetch cadence; long-open tabs still surface new-unlock toasts and
the card picks up the same payload from the shared cache without
issuing a parallel request.

src/app/achievements/page.tsx

@@ -1,6 +1,5 @@
 "use client";
 
-import { useQuery } from "@tanstack/react-query";
 import {
   Activity,
   AlertTriangle,
@@ -36,20 +35,13 @@ import { EmptyState } from "@/components/ui/empty-state";
 import { useAuth } from "@/hooks/use-auth";
 import { useTranslations } from "@/lib/i18n/context";
 import { formatDate } from "@/lib/format";
+import { useAchievementsQuery } from "@/lib/queries/use-achievements-query";
 import {
   ACHIEVEMENT_CATEGORY_ORDER,
   type AchievementCategory,
-  type AchievementMetrics,
   type AchievementProgress,
-  type AchievementSummary,
 } from "@/lib/gamification/achievements";
 
-interface AchievementsData {
-  summary: AchievementSummary;
-  achievements: AchievementProgress[];
-  metrics: AchievementMetrics;
-}
-
 const iconMap: Record<string, LucideIcon> = {
   Activity,
   Flame,
@@ -271,16 +263,11 @@ export default function AchievementsPage() {
   const { isAuthenticated, isLoading: authLoading } = useAuth();
   const { t } = useTranslations();
 
-  const { data, isLoading } = useQuery({
-    queryKey: ["gamification", "achievements"],
-    queryFn: async () => {
-      const res = await fetch("/api/gamification/achievements");
-      if (!res.ok) throw new Error("Failed to load achievements");
-      const json = await res.json();
-      return json.data as AchievementsData;
-    },
-    enabled: isAuthenticated,
-  });
+  // v1.4.34 IW-F-Perf — mother page rides the shared cache slot
+  // alongside `<RecentAchievementsCard>` and
+  // `<AchievementUnlockNotifier>` so the three consumers never trigger
+  // more than one network call on a cold dashboard mount.
+  const { data, isLoading } = useAchievementsQuery();
 
   if (authLoading || isLoading) {
     return (