Add quick-add mode for categories

N (from anywhere) or n (in Category panel) opens an inline prompt
to add categories one after another without typing :add-cat each time.

- Yellow border + prompt distinguishes it from item-add (green)
- Enter / Tab adds the category and clears the buffer, staying open
- Esc returns to the category list
- Cursor automatically moves to the newly added category

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

src/main.rs

@@ -286,6 +286,7 @@ fn draw_status(f: &mut Frame, area: Rect, app: &App) {
         AppMode::FormulaEdit { .. } => "FORMULA",
         AppMode::FormulaPanel => "FORMULAS",
         AppMode::CategoryPanel => "CATEGORIES",
+        AppMode::CategoryAdd { .. } => "NEW CATEGORY",
         AppMode::ItemAdd { .. } => "ADD ITEMS",
         AppMode::ViewPanel => "VIEWS",
         AppMode::TileSelect { .. } => "TILES",