Performance: push ORDER BY/TAKE into SQL for hot-path reads

- IInAppNotificationRepository: typed repo with GetPagedAsync, GetRecentAsync, GetUnreadAsync
  — bell dropdown no longer loads all notifications then slices in C#
- Add compound indexes on InAppNotifications(CompanyId, IsDeleted, CreatedAt) and
  (CompanyId, IsDeleted, IsRead); ContactSubmissions(CompanyId, IsDeleted, CreatedAt)
- PlainRepository.GetAllAsync/FindAsync: add AsNoTracking (Announcements, Tips, ReleaseNotes)
- AiUsageReportController: replace GetAllAsync + C# Where with FindAsync (SQL-level filter)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/PowderCoating.Core/Interfaces/IUnitOfWork.cs

@@ -137,7 +137,7 @@ IRepository<ReworkRecord> ReworkRecords { get; }
     IPlainRepository<Announcement> Announcements { get; }
     IPlainRepository<BannedIp> BannedIps { get; }
     IPlainRepository<DashboardTip> DashboardTips { get; }
-    IRepository<InAppNotification> InAppNotifications { get; }
+    IInAppNotificationRepository InAppNotifications { get; }
     IPlainRepository<ReleaseNote> ReleaseNotes { get; }
 
     // Bug Reports

src/PowderCoating.Core/Interfaces/Repositories/IInAppNotificationRepository.cs

@@ -0,0 +1,32 @@
+using PowderCoating.Core.Entities;
+
+namespace PowderCoating.Core.Interfaces.Repositories;
+
+/// <summary>
+/// Typed repository for <see cref="InAppNotification"/> providing DB-level pagination and
+/// bounded reads for the bell-dropdown and notification history page. The generic
+/// <see cref="IRepository{T}"/> returns materialized lists so ordering/limiting must happen
+/// in C#; these methods push ORDER BY, SKIP, and TAKE into SQL where they belong.
+/// </summary>
+public interface IInAppNotificationRepository : IRepository<InAppNotification>
+{
+    /// <summary>
+    /// Returns a page of notifications ordered newest-first, plus the total un-paged count.
+    /// SuperAdmin path filters to CompanyId == 0 (platform notifications only).
+    /// </summary>
+    Task<(List<InAppNotification> Items, int TotalCount)> GetPagedAsync(
+        bool isPlatformAdmin, int pageNumber, int pageSize);
+
+    /// <summary>
+    /// Returns the <paramref name="take"/> most recent notifications (read and unread)
+    /// for the bell dropdown. SuperAdmin path is scoped to platform notifications.
+    /// </summary>
+    Task<List<InAppNotification>> GetRecentAsync(bool isPlatformAdmin, int take = 20);
+
+    /// <summary>
+    /// Returns the <paramref name="take"/> most recent unread notifications plus the full
+    /// unread count for the bell badge. SuperAdmin path is scoped to platform notifications.
+    /// </summary>
+    Task<(List<InAppNotification> Items, int UnreadCount)> GetUnreadAsync(
+        bool isPlatformAdmin, int take = 20);
+}