Add quick multi-item entry to categories

Two new ways to add multiple items without repeating yourself:

1. :add-items <category> item1 item2 item3 ...
   Adds all space-separated items in one command.

2. Category panel quick-add mode (press 'a' or 'o' on a category):
   - Opens an inline prompt at the bottom of the panel
   - Enter adds the item and clears the buffer — stays open for next entry
   - Tab does the same as Enter
   - Esc closes and returns to the category list
   - The panel border turns green and the title updates to signal add mode
   - Item count in the category list updates live as items are added

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::ItemAdd { .. } => "ADD ITEMS",
         AppMode::ViewPanel => "VIEWS",
         AppMode::TileSelect { .. } => "TILES",
         AppMode::ImportWizard => "IMPORT",