feat: add chat schema and migration

lib/slax/chat/room.ex

@@ -0,0 +1,18 @@
+defmodule Slax.Chat.Room do
+  use Ecto.Schema
+  import Ecto.Changeset
+
+  schema "rooms" do
+    field :name, :string
+    field :topic, :string
+
+    timestamps(type: :utc_datetime)
+  end
+
+  @doc false
+  def changeset(room, attrs) do
+    room
+    |> cast(attrs, [:name, :topic])
+    |> validate_required([:name, :topic])
+  end
+end