fix(message): render messages/_message partial in broadcasts

RubyLLM 1.14.1 added a `to_partial_path` override returning
"messages/<role>" (user/assistant/system/tool). With the bump from
1.11.0 in #102, turbo-rails' `broadcasts_to` stopped finding a partial
because the app only has a single role-aware `_message.html.erb`. Every
message save crashed Turbo::Streams::ActionBroadcastJob with
ActionView::MissingTemplate, silently breaking live chat UI updates for
subscribers (real chats, summaries, testimonials, translations).

Pin the broadcast partial explicitly. Added a regression test that
saves a Message with every role and asserts the enqueued broadcast job
renders cleanly.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: newstler

app/models/message.rb

@@ -1,7 +1,7 @@
 class Message < ApplicationRecord
   acts_as_message tool_calls_foreign_key: :message_id
   has_many_attached :attachments
-  broadcasts_to ->(message) { "chat_#{message.chat_id}" }, inserts_by: :append, target: "messages"
+  broadcasts_to ->(message) { "chat_#{message.chat_id}" }, inserts_by: :append, target: "messages", partial: "messages/message"
 
   after_update_commit :broadcast_message_replacement, if: :assistant?
   before_save :calculate_cost, if: :should_calculate_cost?

test/models/message_test.rb

@@ -1,6 +1,8 @@
 require "test_helper"
 
 class MessageTest < ActiveSupport::TestCase
+  include ActiveJob::TestHelper
+
   test "calculates cost based on token usage" do
     message = Message.new(
       chat: chats(:one),
@@ -15,4 +17,14 @@ class MessageTest < ActiveSupport::TestCase
 
     assert message.cost > 0
   end
+
+  test "broadcasts create using messages/message partial regardless of role" do
+    %w[user assistant system tool].each do |role|
+      message = Message.new(chat: chats(:one), role: role, content: "hi")
+
+      assert_nothing_raised do
+        perform_enqueued_jobs { message.save! }
+      end
+    end
+  end
 end