Add first version of online stores for wishlisted records (claude)

See docs/plans/online_stores.md

lib/music_library/online_store_templates/online_store_template.ex

@@ -0,0 +1,37 @@
+defmodule MusicLibrary.OnlineStoreTemplates.OnlineStoreTemplate do
+  use Ecto.Schema
+  import Ecto.Changeset
+
+  @primary_key {:id, :binary_id, autogenerate: true}
+  @foreign_key_type :binary_id
+
+  schema "online_store_templates" do
+    field :name, :string
+    field :description, :string
+    field :url_template, :string
+    field :enabled, :boolean, default: true
+
+    timestamps(type: :utc_datetime)
+  end
+
+  @doc false
+  def changeset(template, attrs) do
+    template
+    |> cast(attrs, [:name, :description, :url_template, :enabled])
+    |> validate_required([:name, :url_template])
+    |> validate_length(:name, min: 1, max: 100)
+    |> validate_length(:url_template, min: 1, max: 500)
+    |> validate_url_template()
+  end
+
+  defp validate_url_template(changeset) do
+    if template = get_field(changeset, :url_template) do
+      case URI.parse(template) do
+        %URI{scheme: scheme} when scheme in ["http", "https"] -> changeset
+        _ -> add_error(changeset, :url_template, "must be a valid HTTP or HTTPS URL")
+      end
+    else
+      changeset
+    end
+  end
+end