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.Infrastructure/Repositories/InAppNotificationRepository.cs

@@ -0,0 +1,83 @@
+using Microsoft.EntityFrameworkCore;
+using PowderCoating.Core.Entities;
+using PowderCoating.Core.Interfaces.Repositories;
+using PowderCoating.Infrastructure.Data;
+
+namespace PowderCoating.Infrastructure.Repositories;
+
+/// <summary>
+/// Typed repository for <see cref="InAppNotification"/>. Overrides the three hot-path
+/// read operations so ORDER BY / SKIP / TAKE run in SQL rather than in C# after a full
+/// table load — critical for the bell dropdown (Recent/Unread) which fires on every page.
+/// </summary>
+public class InAppNotificationRepository
+    : Repository<InAppNotification>, IInAppNotificationRepository
+{
+    public InAppNotificationRepository(ApplicationDbContext context) : base(context) { }
+
+    /// <inheritdoc/>
+    public async Task<(List<InAppNotification> Items, int TotalCount)> GetPagedAsync(
+        bool isPlatformAdmin, int pageNumber, int pageSize)
+    {
+        // SuperAdmin path: bypass global filters, scope to CompanyId 0 (platform-only).
+        // Regular path: global filter already scopes to the current tenant.
+        var query = isPlatformAdmin
+            ? _context.Set<InAppNotification>()
+                .IgnoreQueryFilters()
+                .Where(n => !n.IsDeleted && n.CompanyId == 0)
+            : _context.Set<InAppNotification>()
+                .Where(n => true);
+
+        var totalCount = await query.CountAsync();
+
+        var items = await query
+            .AsNoTracking()
+            .OrderByDescending(n => n.CreatedAt)
+            .Skip((pageNumber - 1) * pageSize)
+            .Take(pageSize)
+            .ToListAsync();
+
+        return (items, totalCount);
+    }
+
+    /// <inheritdoc/>
+    public async Task<List<InAppNotification>> GetRecentAsync(
+        bool isPlatformAdmin, int take = 20)
+    {
+        var query = isPlatformAdmin
+            ? _context.Set<InAppNotification>()
+                .IgnoreQueryFilters()
+                .Where(n => !n.IsDeleted && n.CompanyId == 0)
+            : _context.Set<InAppNotification>()
+                .Where(n => true);
+
+        return await query
+            .AsNoTracking()
+            .OrderByDescending(n => n.CreatedAt)
+            .Take(take)
+            .ToListAsync();
+    }
+
+    /// <inheritdoc/>
+    public async Task<(List<InAppNotification> Items, int UnreadCount)> GetUnreadAsync(
+        bool isPlatformAdmin, int take = 20)
+    {
+        // Count ALL unread for the badge, then cap the items list for the dropdown.
+        var baseQuery = isPlatformAdmin
+            ? _context.Set<InAppNotification>()
+                .IgnoreQueryFilters()
+                .Where(n => !n.IsDeleted && n.CompanyId == 0 && !n.IsRead)
+            : _context.Set<InAppNotification>()
+                .Where(n => !n.IsRead);
+
+        var unreadCount = await baseQuery.CountAsync();
+
+        var items = await baseQuery
+            .AsNoTracking()
+            .OrderByDescending(n => n.CreatedAt)
+            .Take(take)
+            .ToListAsync();
+
+        return (items, unreadCount);
+    }
+}

src/PowderCoating.Infrastructure/Repositories/PlainRepository.cs

@@ -26,10 +26,10 @@ public class PlainRepository<T> : IPlainRepository<T> where T : class
         => await _dbSet.FindAsync(id);
 
     public virtual async Task<IEnumerable<T>> GetAllAsync()
-        => await _dbSet.ToListAsync();
+        => await _dbSet.AsNoTracking().ToListAsync();
 
     public virtual async Task<IEnumerable<T>> FindAsync(Expression<Func<T, bool>> predicate)
-        => await _dbSet.Where(predicate).ToListAsync();
+        => await _dbSet.AsNoTracking().Where(predicate).ToListAsync();
 
     public virtual async Task<T?> FirstOrDefaultAsync(Expression<Func<T, bool>> predicate)
         => await _dbSet.FirstOrDefaultAsync(predicate);

src/PowderCoating.Infrastructure/Repositories/UnitOfWork.cs

@@ -109,7 +109,7 @@ public class UnitOfWork : IUnitOfWork
     private IPlainRepository<Announcement>? _announcements;
     private IPlainRepository<BannedIp>? _bannedIps;
     private IPlainRepository<DashboardTip>? _dashboardTips;
-    private IRepository<InAppNotification>? _inAppNotifications;
+    private IInAppNotificationRepository? _inAppNotifications;
     private IPlainRepository<ReleaseNote>? _releaseNotes;
 
     // Bug Reports
@@ -439,8 +439,8 @@ public class UnitOfWork : IUnitOfWork
         _dashboardTips ??= new PlainRepository<DashboardTip>(_context);
 
     /// <summary>Repository for <see cref="InAppNotification"/> bell-notification records; tenant-filtered with soft delete.</summary>
-    public IRepository<InAppNotification> InAppNotifications =>
-        _inAppNotifications ??= new Repository<InAppNotification>(_context);
+    public IInAppNotificationRepository InAppNotifications =>
+        _inAppNotifications ??= new InAppNotificationRepository(_context);
 
     /// <summary>Repository for <see cref="ReleaseNote"/> platform changelog entries; no tenant filter, no soft delete.</summary>
     public IPlainRepository<ReleaseNote> ReleaseNotes =>