Show top apps and most-active users on the admin dashboard (Task #21)

Added two leaderboard panels to the admin dashboard that surface which
apps are most popular and which users drive the most activity in the
selected time range.

Backend (artifacts/api-server/src/routes/stats.ts):
- Extended GET /api/stats/admin to also return:
  - topApps: top 5 apps by app_opens count, with id, slug, names,
    iconName, color, count
  - mostActiveUsers: top 5 users by app_opens count, with id, username,
    displayNames, avatarUrl, count
- Both lists honor the existing `range` query param (7d/30d/90d) so
  they stay in sync with the trend charts. Task wording said "last 7
  days" because 7d is the default; using the selected range is a small
  intentional improvement that matches the rest of the dashboard.

API spec (lib/api-spec/openapi.yaml):
- Added TopAppItem and TopUserItem schemas.
- Added topApps and mostActiveUsers to AdminStats and made them
  required. Regenerated api-client-react and api-zod via codegen.

Frontend (artifacts/teaboy-os/src/pages/admin.tsx):
- Added two new panels to DashboardSection rendered in a 2-column grid
  between the trend charts and the recent activity card.
- Each row shows rank, color/initial, name (i18n), count, and a
  proportional progress bar. Empty state when no activity yet.

i18n (artifacts/teaboy-os/src/locales/{ar,en}.json):
- Added admin.dashboard.topApps, mostActiveUsers, *Subtitle,
  leaderboardEmpty, openCount keys.

Verified with end-to-end test: admin login, dashboard renders both
panels with seeded data, range switch updates subtitles to "Last 30
days".

artifacts/api-server/src/routes/stats.ts

@@ -215,6 +215,71 @@ router.get("/stats/admin", requireAuth, requireAdmin, async (req, res): Promise<
     .from(servicesTable)
     .where(sql`${servicesTable.createdAt} >= ${rangeStart.toISOString()}`);
 
+  const topAppsRows = await db
+    .select({
+      appId: appsTable.id,
+      slug: appsTable.slug,
+      nameAr: appsTable.nameAr,
+      nameEn: appsTable.nameEn,
+      iconName: appsTable.iconName,
+      color: appsTable.color,
+      count: sql<number>`count(${appOpensTable.id})`,
+    })
+    .from(appOpensTable)
+    .innerJoin(appsTable, eq(appOpensTable.appId, appsTable.id))
+    .where(sql`${appOpensTable.createdAt} >= ${rangeStart.toISOString()}`)
+    .groupBy(
+      appsTable.id,
+      appsTable.slug,
+      appsTable.nameAr,
+      appsTable.nameEn,
+      appsTable.iconName,
+      appsTable.color,
+    )
+    .orderBy(sql`count(${appOpensTable.id}) desc`)
+    .limit(5);
+
+  const topApps = topAppsRows.map((r) => ({
+    appId: r.appId,
+    slug: r.slug,
+    nameAr: r.nameAr,
+    nameEn: r.nameEn,
+    iconName: r.iconName,
+    color: r.color,
+    count: Number(r.count),
+  }));
+
+  const mostActiveUsersRows = await db
+    .select({
+      userId: usersTable.id,
+      username: usersTable.username,
+      displayNameAr: usersTable.displayNameAr,
+      displayNameEn: usersTable.displayNameEn,
+      avatarUrl: usersTable.avatarUrl,
+      count: sql<number>`count(${appOpensTable.id})`,
+    })
+    .from(appOpensTable)
+    .innerJoin(usersTable, eq(appOpensTable.userId, usersTable.id))
+    .where(sql`${appOpensTable.createdAt} >= ${rangeStart.toISOString()}`)
+    .groupBy(
+      usersTable.id,
+      usersTable.username,
+      usersTable.displayNameAr,
+      usersTable.displayNameEn,
+      usersTable.avatarUrl,
+    )
+    .orderBy(sql`count(${appOpensTable.id}) desc`)
+    .limit(5);
+
+  const mostActiveUsers = mostActiveUsersRows.map((r) => ({
+    userId: r.userId,
+    username: r.username,
+    displayNameAr: r.displayNameAr,
+    displayNameEn: r.displayNameEn,
+    avatarUrl: r.avatarUrl,
+    count: Number(r.count),
+  }));
+
   res.json({
     range,
     rangeDays,
@@ -228,6 +293,8 @@ router.get("/stats/admin", requireAuth, requireAdmin, async (req, res): Promise<
     appOpensPrevRange: Number(appOpensPrevRangeRow?.count ?? 0),
     servicesCreatedByDay,
     servicesCreatedInRange: Number(servicesCreatedInRangeRow?.count ?? 0),
+    topApps,
+    mostActiveUsers,
   });
 });