Add automatic PostgreSQL database creation and migration

- Added Jellyfin.Database.Providers.Postgres project with full EF Core migration support for PostgreSQL.
- Implemented automatic database creation and privilege assignment on startup.
- Generated initial migration and model snapshot for PostgreSQL schema.
- Updated build, test, and dependency files to include PostgreSQL provider and Npgsql packages.
- Added PowerShell script for generating and testing PostgreSQL migrations.
- No changes to application logic outside database provider/migration infrastructure.

src/Jellyfin.Database/Jellyfin.Database.Providers.Postgres/PostgresDatabaseProvider.cs

@@ -97,6 +97,94 @@ public sealed class PostgresDatabaseProvider : IJellyfinDatabaseProvider
         }
     }
 
+    /// <summary>
+    /// Ensures the PostgreSQL database exists, creating it if necessary.
+    /// </summary>
+    /// <param name="databaseConfiguration">The database configuration.</param>
+    /// <param name="cancellationToken">Cancellation token.</param>
+    /// <returns>A task representing the asynchronous operation.</returns>
+    public async Task EnsureDatabaseExistsAsync(DatabaseConfigurationOptions databaseConfiguration, CancellationToken cancellationToken = default)
+    {
+        static T? GetOption<T>(ICollection<CustomDatabaseOption>? options, string key, Func<string, T> converter, Func<T>? defaultValue = null)
+        {
+            if (options is null)
+            {
+                return defaultValue is not null ? defaultValue() : default;
+            }
+
+            var value = options.FirstOrDefault(e => e.Key.Equals(key, StringComparison.OrdinalIgnoreCase));
+            if (value is null)
+            {
+                return defaultValue is not null ? defaultValue() : default;
+            }
+
+            return converter(value.Value);
+        }
+
+        var customOptions = databaseConfiguration.CustomProviderOptions?.Options;
+
+        var host = GetOption(customOptions, "host", e => e, () => "localhost")!;
+        var port = GetOption(customOptions, "port", int.Parse, () => 5432);
+        var database = GetOption(customOptions, "database", e => e, () => "jellyfin")!;
+        var username = GetOption(customOptions, "username", e => e, () => "jellyfin")!;
+        var password = GetOption(customOptions, "password", e => e, () => string.Empty)!;
+        var timeout = GetOption(customOptions, "connection-timeout", int.Parse, () => 15);
+
+        // Connect to 'postgres' maintenance database to check if target database exists
+        var maintenanceConnectionBuilder = new NpgsqlConnectionStringBuilder
+        {
+            Host = host,
+            Port = port,
+            Database = "postgres", // Connect to maintenance database
+            Username = username,
+            Password = password,
+            Timeout = timeout,
+            Pooling = false // Don't pool maintenance connections
+        };
+
+        try
+        {
+            await using var connection = new NpgsqlConnection(maintenanceConnectionBuilder.ToString());
+            await connection.OpenAsync(cancellationToken).ConfigureAwait(false);
+
+            // Check if database exists
+            var checkQuery = "SELECT 1 FROM pg_database WHERE datname = @databaseName";
+            await using var checkCommand = new NpgsqlCommand(checkQuery, connection);
+            checkCommand.Parameters.AddWithValue("databaseName", database);
+
+            var exists = await checkCommand.ExecuteScalarAsync(cancellationToken).ConfigureAwait(false);
+
+            if (exists is null)
+            {
+                // Database doesn't exist, create it
+                logger.LogInformation("PostgreSQL database '{Database}' does not exist. Creating...", database);
+
+                // Use identifier quoting for safety
+                var createQuery = $"CREATE DATABASE \"{database}\" OWNER \"{username}\"";
+                await using var createCommand = new NpgsqlCommand(createQuery, connection);
+                await createCommand.ExecuteNonQueryAsync(cancellationToken).ConfigureAwait(false);
+
+                logger.LogInformation("PostgreSQL database '{Database}' created successfully", database);
+
+                // Grant privileges
+                var grantQuery = $"GRANT ALL PRIVILEGES ON DATABASE \"{database}\" TO \"{username}\"";
+                await using var grantCommand = new NpgsqlCommand(grantQuery, connection);
+                await grantCommand.ExecuteNonQueryAsync(cancellationToken).ConfigureAwait(false);
+
+                logger.LogInformation("Granted all privileges on database '{Database}' to user '{Username}'", database, username);
+            }
+            else
+            {
+                logger.LogInformation("PostgreSQL database '{Database}' already exists", database);
+            }
+        }
+        catch (Exception ex)
+        {
+            logger.LogError(ex, "Failed to ensure PostgreSQL database '{Database}' exists. Error: {Message}", database, ex.Message);
+            throw;
+        }
+    }
+
     /// <inheritdoc/>
     public async Task RunScheduledOptimisation(CancellationToken cancellationToken)
     {