Add automated PostgreSQL performance index management

- Add scripts and SQL for base and supplementary indexes (total 23)
- Integrate index checks and auto-creation into Jellyfin startup
- Update csproj to include SQL files in build/publish output
- Add diagnostics, publish/copy scripts, and troubleshooting docs
- Provide detailed guides for migration, verification, and merging
- Ensures robust, automated, and well-documented index setup

Jellyfin.Server.Implementations/Database/SupplementaryIndexChecker.cs

@@ -0,0 +1,79 @@
+// <copyright file="SupplementaryIndexChecker.cs" company="PlaceholderCompany">
+// Copyright (c) PlaceholderCompany. All rights reserved.
+// </copyright>
+
+namespace Jellyfin.Server.Implementations.Database;
+
+using System;
+using System.Threading;
+using System.Threading.Tasks;
+using Microsoft.EntityFrameworkCore;
+using Microsoft.Extensions.Logging;
+using Npgsql;
+
+/// <summary>
+/// Ensures supplementary performance indexes exist on database startup.
+/// </summary>
+public class SupplementaryIndexChecker
+{
+    private readonly ILogger<SupplementaryIndexChecker> _logger;
+    private readonly DbContext _context;
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="SupplementaryIndexChecker"/> class.
+    /// </summary>
+    /// <param name="logger">The logger.</param>
+    /// <param name="context">The database context.</param>
+    public SupplementaryIndexChecker(ILogger<SupplementaryIndexChecker> logger, DbContext context)
+    {
+        _logger = logger;
+        _context = context;
+    }
+
+    /// <summary>
+    /// Checks if supplementary indexes exist and logs warnings if they don't.
+    /// </summary>
+    /// <param name="cancellationToken">Cancellation token.</param>
+    /// <returns>True if all indexes exist, false otherwise.</returns>
+    public async Task<bool> CheckSupplementaryIndexesAsync(CancellationToken cancellationToken = default)
+    {
+        try
+        {
+            var connection = _context.Database.GetDbConnection();
+            await connection.OpenAsync(cancellationToken).ConfigureAwait(false);
+
+            var checkQuery = @"
+                SELECT COUNT(*) 
+                FROM pg_indexes 
+                WHERE indexname IN (
+                    'idx_baseitems_type_isvirtualitem_topparentid',
+                    'idx_baseitems_topparentid_isfolder',
+                    'idx_baseitems_datecreated_filtered',
+                    'idx_itemvaluesmap_itemvalueid_itemid',
+                    'idx_activitylogs_userid_datecreated'
+                )";
+
+            await using var command = connection.CreateCommand();
+            command.CommandText = checkQuery;
+            var result = await command.ExecuteScalarAsync(cancellationToken).ConfigureAwait(false);
+            var indexCount = Convert.ToInt32(result);
+
+            if (indexCount < 5)
+            {
+                _logger.LogWarning(
+                    "Only {IndexCount}/5 supplementary performance indexes found. " +
+                    "Run 'sql/schema_init/10_create_supplementary_indexes.sql' to add missing indexes for better performance.",
+                    indexCount);
+                return false;
+            }
+
+            _logger.LogInformation("All supplementary performance indexes are present ({IndexCount}/5).", indexCount);
+            return true;
+        }
+        catch (Exception ex)
+        {
+            _logger.LogError(ex, "Failed to check supplementary indexes");
+            return false;
+        }
+    }
+}