fix(ha): register IServerConfigurationManager in pre-startup DI for PostgreSQL

The NpgsqlDataSource singleton factory in AddJellyfinDbContext calls
sp.GetRequiredService<IServerConfigurationManager>() to read pool settings.
During ApplyStartupMigrationAsync, only a subset of services are registered
in the startup service collection — IServerConfigurationManager was missing,
causing a fatal DI resolution failure when DatabaseType=Jellyfin-PostgreSQL.

Fix: register startupConfigurationManager as IServerConfigurationManager in
the migrationStartupServiceProvider service collection.

Also remove JELLYFIN_CONFIG_DIR=/config from Dockerfile.runtime ENV block.
When configDir == dataDir, MakeSanityCheckOrThrow writes .jellyfin-config at
the datadir root, then immediately throws because it expected .jellyfin-data.
Removing the env var lets configDir default to $JELLYFIN_DATA_DIR/config.

Jellyfin.Server/Program.cs

@@ -285,6 +285,10 @@ namespace Jellyfin.Server
                 .AddJellyfinDbContext(startupConfigurationManager, startupConfig)
                 .AddSingleton<IApplicationPaths>(appPaths)
                 .AddSingleton<ServerApplicationPaths>(appPaths)
+                // Required by NpgsqlDataSource factory in AddJellyfinDbContext when
+                // DatabaseType=Jellyfin-PostgreSQL — the factory resolves this from DI
+                // to read CustomProviderOptions and pool settings.
+                .AddSingleton<IServerConfigurationManager>(startupConfigurationManager)
                 .RegisterStartupLogger();
 
             migrationStartupServiceProvider.AddSingleton(migrationStartupServiceProvider);