Fix API controller tests: 404 handling, JSON encoding, media filtering

- Add FallbackController for proper 404 JSON responses on missing resources
- Add non-bang get_source/1 and get_media_item/1 for safe lookups
- Fix Task JSON encoder: remove Repo.preload call (not available in encoder scope),
  handle NotLoaded associations by returning nil
- Fix media item index: use list_media_items_for_source/1 instead of
  list_pending_media_items_for/1 which had overly restrictive filtering
- Add missing extras_directory to test config
- All 1007 tests pass

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

@@ -5,6 +5,8 @@ defmodule PinchflatWeb.Api.V1.ApiSourceController do
 
   use PinchflatWeb, :controller
 
+  action_fallback PinchflatWeb.Api.V1.FallbackController
+
   alias Pinchflat.Repo
   alias Pinchflat.Sources
   alias Pinchflat.Sources.Source
@@ -21,14 +23,20 @@ defmodule PinchflatWeb.Api.V1.ApiSourceController do
   end
 
   def show(conn, %{"id" => id}) do
-    source = Sources.get_source!(id) |> Repo.preload([:media_profile, :media_items])
+    case Sources.get_source(id) do
+      nil ->
+        {:error, :not_found}
 
-    pending_tasks =
-      source
-      |> Tasks.list_tasks_for(nil, [:executing, :available, :scheduled, :retryable])
-      |> Repo.preload(:job)
+      source ->
+        source = Repo.preload(source, [:media_profile, :media_items])
 
-    json(conn, %{data: source, pending_tasks: pending_tasks})
+        pending_tasks =
+          source
+          |> Tasks.list_tasks_for(nil, [:executing, :available, :scheduled, :retryable])
+          |> Repo.preload(:job)
+
+        json(conn, %{data: source, pending_tasks: pending_tasks})
+    end
   end
 
   def create(conn, %{"source" => source_params}) do