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".

Replit-Task-Id: c7b6aa4b-9242-443b-9802-a39ab0bc9547

lib/api-spec/openapi.yaml

@@ -1607,6 +1607,14 @@ components:
               - count
         servicesCreatedInRange:
           type: integer
+        topApps:
+          type: array
+          items:
+            $ref: "#/components/schemas/TopAppItem"
+        mostActiveUsers:
+          type: array
+          items:
+            $ref: "#/components/schemas/TopUserItem"
       required:
         - range
         - rangeDays
@@ -1620,3 +1628,51 @@ components:
         - appOpensPrevRange
         - servicesCreatedByDay
         - servicesCreatedInRange
+        - topApps
+        - mostActiveUsers
+
+    TopAppItem:
+      type: object
+      properties:
+        appId:
+          type: integer
+        slug:
+          type: string
+        nameAr:
+          type: string
+        nameEn:
+          type: string
+        iconName:
+          type: string
+        color:
+          type: string
+        count:
+          type: integer
+      required:
+        - appId
+        - slug
+        - nameAr
+        - nameEn
+        - iconName
+        - color
+        - count
+
+    TopUserItem:
+      type: object
+      properties:
+        userId:
+          type: integer
+        username:
+          type: string
+        displayNameAr:
+          type: ["string", "null"]
+        displayNameEn:
+          type: ["string", "null"]
+        avatarUrl:
+          type: ["string", "null"]
+        count:
+          type: integer
+      required:
+        - userId
+        - username
+        - count