Add GET /workflow/upcoming endpoint that reads .story_kit/stories/upcoming/
and returns story IDs with names parsed from frontmatter. Add UpcomingPanel
component wired into Chat view with loading, error, empty, and list states.
12 new tests (3 backend, 9 frontend) all passing.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
