Story 31: View Upcoming Stories

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>

server/src/http/context.rs

@@ -11,6 +11,20 @@ pub struct AppContext {
     pub workflow: Arc<std::sync::Mutex<WorkflowState>>,
 }
 
+#[cfg(test)]
+impl AppContext {
+    pub fn new_test(project_root: std::path::PathBuf) -> Self {
+        let state = SessionState::default();
+        *state.project_root.lock().unwrap() = Some(project_root.clone());
+        let store_path = project_root.join(".story_kit_store.json");
+        Self {
+            state: Arc::new(state),
+            store: Arc::new(JsonFileStore::new(store_path).unwrap()),
+            workflow: Arc::new(std::sync::Mutex::new(WorkflowState::default())),
+        }
+    }
+}
+
 pub type OpenApiResult<T> = poem::Result<T>;
 
 pub fn bad_request(message: String) -> poem::Error {