Postgres perf, path migration, and shutdown race fixes

- Major query performance boost: replaced correlated subqueries with DistinctBy() in BaseItemRepository, added episode deduplication index, and increased default command timeout to 120s.
- Fixed LibraryMonitor shutdown race: added disposal checks and exception handling in FileRefresher to prevent ObjectDisposedException.
- Added PowerShell and SQL utilities for fixing Linux paths in config files and database; new scripts for WebDir and path migration.
- Auto-fix for WebDir in startup.json on load; new helper scripts and docs.
- Added automated weekly DB performance monitoring scripts and reporting.
- Expanded documentation and README for all fixes, scripts, and migration steps.
- Updated SQL scripts for index creation and diagnostics; improved output handling.
- Updated db-config defaults and added new diagnostic/report files.

Jellyfin.Server/Helpers/StartupHelpers.cs

@@ -70,6 +70,45 @@ public static class StartupHelpers
         logger.LogInformation("Application directory: {ApplicationPath}", appPaths.ProgramSystemPath);
     }
 
+    /// <summary>
+    /// Fixes incorrect absolute WebDir paths in startup.json to use relative paths.
+    /// This handles legacy configurations that used absolute paths like "C:/ProgramData/jellyfin/wwwroot".
+    /// </summary>
+    /// <param name="configPath">Path to the startup.json file.</param>
+    private static void FixWebDirPath(string configPath)
+    {
+        try
+        {
+            var content = File.ReadAllText(configPath);
+            var originalContent = content;
+
+            // Fix Windows absolute paths
+            content = System.Text.RegularExpressions.Regex.Replace(
+                content,
+                @"""WebDir"":\s*""[^""]*[/\\]jellyfin[/\\](?:data[/\\])?wwwroot""",
+                @"""WebDir"": ""wwwroot""",
+                System.Text.RegularExpressions.RegexOptions.IgnoreCase);
+
+            // Fix Linux absolute paths
+            content = System.Text.RegularExpressions.Regex.Replace(
+                content,
+                @"""WebDir"":\s*""[^""]*[/\\]usr[/\\]share[/\\]jellyfin[/\\]wwwroot""",
+                @"""WebDir"": ""wwwroot""",
+                System.Text.RegularExpressions.RegexOptions.IgnoreCase);
+
+            // Only write if changed
+            if (content != originalContent)
+            {
+                File.WriteAllText(configPath, content);
+                Console.WriteLine($"Fixed WebDir path in: {configPath}");
+            }
+        }
+        catch (Exception ex)
+        {
+            Console.WriteLine($"Warning: Could not fix WebDir path in {configPath}: {ex.Message}");
+        }
+    }
+
     /// <summary>
     /// Loads startup configuration from startup.json file if it exists.
     /// If no configuration file exists, creates a default one in the application directory.
@@ -93,6 +132,9 @@ public static class StartupHelpers
             {
                 try
                 {
+                    // Check and fix incorrect WebDir paths before loading
+                    FixWebDirPath(configPath);
+
                     var config = new ConfigurationBuilder()
                         .AddJsonFile(configPath, optional: false, reloadOnChange: false)
                         .Build();