Wire the inline boost link to the soft keyboard

link_to passed `action: "soft-keyboard#open"` as a plain option, so it
rendered as an `action` attribute, which Stimulus never reads. The link
in messages/_actions.html.erb already passes it under `data:`; this one
now does too, so tapping "Add a boost" on a touch device opens the
keyboard for the boost form as the menu's link does.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

test/controllers/messages/boosts_controller_test.rb

@@ -6,6 +6,13 @@ class Messages::BoostsControllerTest < ActionDispatch::IntegrationTest
     @message = messages(:first)
   end
 
+  test "index wires the new boost link to the soft keyboard" do
+    get message_boosts_url(@message)
+
+    assert_response :success
+    assert_select ".message__boost-inline a.boost__action[data-action='soft-keyboard#open']"
+  end
+
   test "create" do
     assert_turbo_stream_broadcasts [ @message.room, :messages ], count: 1 do
       assert_difference -> { @message.boosts.count }, 1 do