Add Dockerfile-based Dokku deployment for monorepo layout

Uses a multi-stage Docker build that copies both app/ and blogex/,
preserving the path dependency. Includes release scripts, migration
module, and a sample Dokku setup script.

app/lib/firehose/release.ex

@@ -0,0 +1,31 @@
+defmodule Firehose.Release do
+  @moduledoc """
+  Tasks for production releases (e.g., database migrations).
+
+  Usage from Dokku:
+      dokku run APP_NAME /app/bin/migrate
+  """
+
+  @app :firehose
+
+  def migrate do
+    load_app()
+
+    for repo <- repos() do
+      {:ok, _, _} = Ecto.Migrator.with_repo(repo, &Ecto.Migrator.run(&1, :up, all: true))
+    end
+  end
+
+  def rollback(repo, version) do
+    load_app()
+    {:ok, _, _} = Ecto.Migrator.with_repo(repo, &Ecto.Migrator.run(&1, :down, to: version))
+  end
+
+  defp repos do
+    Application.fetch_env!(@app, :ecto_repos)
+  end
+
+  defp load_app do
+    Application.load(@app)
+  end
+end