Drop the unused project description field entirely

It never got a UI home on the frontend -- removed from ProjectView a
few sessions back and never restored anywhere -- so it was a fully
live field (validated, stored, returned by the API, covered by tests)
with no consumer.

- Migration 011: ALTER TABLE projects DROP COLUMN description.
- ProjectRepository: description dropped from ProjectRow, SELECT,
  create() and update() -- update() is now just a rename (string, not
  a $fields array; there was never more than one editable field once
  this left).
- ProjectController: store()/update() no longer accept or validate
  it; update() drops the "provide at least one of title, description"
  branch, since title is unconditionally the only field now.
- Frontend Project type, root README's API docs and curl example.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/Http/Controllers/ProjectScopedController.php

@@ -24,7 +24,7 @@ abstract class ProjectScopedController extends Controller
      * by the authenticated user.
      *
      * @param array<string, string> $args
-     * @return array{id: int, owner_id: int, title: string, description: string, card_count: int, completed_count: int, created_at: string, updated_at: string}
+     * @return array{id: int, owner_id: int, title: string, card_count: int, completed_count: int, created_at: string, updated_at: string}
      */
     protected function requireOwnedProject(Request $request, array $args): array
     {