Fix CI: remove unused aliases, run mix format, install root yarn deps

- Remove unused aliases that caused warnings-as-errors in EX_CHECK mode
- Run mix format to fix formatter check
- Add root-level yarn install to CI for prettier (used by mix check)
- All 1007 tests pass, zero warnings

lib/pinchflat_web/controllers/api/v1/api_task_controller.ex

@@ -15,6 +15,7 @@ defmodule PinchflatWeb.Api.V1.ApiTaskController do
       case params do
         %{"source_id" => source_id} ->
           source = Pinchflat.Sources.get_source!(source_id)
+
           Tasks.list_tasks_for(source)
           |> Repo.preload(:job)
 
@@ -30,4 +31,4 @@ defmodule PinchflatWeb.Api.V1.ApiTaskController do
     task = Tasks.get_task!(id) |> Repo.preload(:job)
     json(conn, %{data: task})
   end
-end
+end