chore: remove keyboard navigation UI elements and related code

- Delete static/css/components/keyboard-nav.css entirely
- Remove @import of keyboard-nav.css from style.css
- Remove keyboard-nav-hint divs from controls.html and recipes.html
- Clean up all keyboard.* translation keys from 10 locale files

The actual keyboard scrolling handlers (PageUp/PageDown in infiniteScroll.js
and VirtualScroller.js) are kept as they provide core scroll functionality.

locales/he.json

@@ -1424,15 +1424,6 @@
             "duplicate": "תגית זו כבר קיימת"
         }
     },
-    "keyboard": {
-        "navigation": "ניווט במקלדת:",
-        "shortcuts": {
-            "pageUp": "גלול עמוד אחד למעלה",
-            "pageDown": "גלול עמוד אחד למטה",
-            "home": "קפוץ להתחלה",
-            "end": "קפוץ לסוף"
-        }
-    },
     "initialization": {
         "title": "מאתחל",
         "message": "מכין את סביבת העבודה שלך...",