style: replace em dashes with hyphens throughout codebase

Replace all — with - in all source files (JS, CSS, HTML, JSON,
Markdown) for consistency and readability.

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

test-meals.js

@@ -251,7 +251,7 @@ test('Zutaten → Einkaufsliste übertragen (INSERT + Flag setzen)', () => {
 });
 
 test('Zweiter Transfer überträgt nichts (alle bereits markiert)', () => {
-  // Mahlzeit aus vorherigem Test — alle on_shopping_list = 1
+  // Mahlzeit aus vorherigem Test - alle on_shopping_list = 1
   const suppe = db.prepare(`SELECT id FROM meals WHERE title = 'Suppe'`).get();
   const open = db.prepare(`
     SELECT * FROM meal_ingredients WHERE meal_id = ? AND on_shopping_list = 0