Add database backup functionality

lib/music_library_web/controllers/archive_controller.ex

@@ -0,0 +1,18 @@
+defmodule MusicLibraryWeb.ArchiveController do
+  use MusicLibraryWeb, :controller
+
+  def backup(conn, _params) do
+    database_path = database_path()
+    current_time = DateTime.utc_now()
+    file_name = "music_library_#{DateTime.to_unix(current_time)}.db"
+
+    send_download(conn, {:file, database_path},
+      filename: file_name,
+      content_type: "application/x-sqlite3"
+    )
+  end
+
+  defp database_path do
+    Application.get_env(:music_library, MusicLibrary.Repo)[:database]
+  end
+end