feat: add Missing Class / Launch tab to Article Details

Adds a new 'Missing Class / Launch' tab in Article Details that surfaces
items where Classification is empty or Launch Date is blank/01-01-1900.
The tab shows Classification, Launch Date, and Ready to Order columns for
quick reference. Column indices for Launch Date and Ready to Order are
resolved dynamically from the Excel headers.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/App.tsx

@@ -548,6 +548,7 @@ export default function App() {
               {activeModule === 'article_details' && (
                 <ArticleDetails
                   data={appState.data}
+                  headers={appState.headers}
                   onEdit={(index) => setEditingRowIndex(index)}
                   rowStatuses={rowStatuses}
                 />