Add JSON REST API for MCP integration

- Add /api/v1 namespace with Bearer token auth (PINCHFLAT_API_TOKEN env var)
- API controllers for sources, media items, media profiles, settings, tasks
- Support for all source actions: create, update, delete, force_download_pending,
  force_redownload, force_index, force_metadata_refresh, sync_files_on_disk
- Media item endpoints: list, show, search, force_download, update, delete
- Media profile CRUD endpoints
- Settings show/update and app_info endpoints
- Task listing endpoints
- Add Jason.Encoder for Task schema
- Comprehensive test suite for all API endpoints
- Gitea Actions CI workflow (runs existing checks + API-specific tests)
- API documentation in docs/API.md

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

@@ -0,0 +1,31 @@
+defmodule PinchflatWeb.Api.V1.ApiTaskController do
+  @moduledoc """
+  JSON API controller for Tasks.
+  """
+
+  use PinchflatWeb, :controller
+
+  alias Pinchflat.Repo
+  alias Pinchflat.Tasks
+
+  def index(conn, params) do
+    tasks =
+      case params do
+        %{"source_id" => source_id} ->
+          source = Pinchflat.Sources.get_source!(source_id)
+          Tasks.list_tasks_for(source)
+          |> Repo.preload(:job)
+
+        _ ->
+          Tasks.list_tasks()
+          |> Repo.preload(:job)
+      end
+
+    json(conn, %{data: tasks})
+  end
+
+  def show(conn, %{"id" => id}) do
+    task = Tasks.get_task!(id) |> Repo.preload(:job)
+    json(conn, %{data: task})
+  end
+end