XL landscape polish: btn-primary sizing, tray from right, footer bg, layout fixes

- .btn-xl removed; .btn-primary absorbs 4rem sizing (same as PICK SIGS/PICK ROLES)
- Landscape navbar .btn-primary: 3rem → 4rem to match base; XL stays 4rem (consistent)
- _button-pad.scss XL: base .btn ×1.2 (2.4rem); .btn-xl block deleted
- _tray.scss XL (≥1800px): portrait-style tray (slides from right, z-95)
- tray.js: _isLandscape() returns false at ≥1800px; portrait code paths run throughout
- Footer sidebar: background-color added so opaque footer masks tray sliding behind it
- Copyright .footer-container: bottom → top in landscape sidebar
- #id_room_menu: right: 2.5rem override in _room.scss XL block (cascade fix)
- navbar-text XL: 0.65rem × 1.2 = 0.78rem
- All landscape media queries: max-width: 1440px cutoff removed (already done prior)
- btn-xl class stripped from all 5 templates; test_navbar.py assertion updated

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

src/static_src/scss/_game-kit.scss

@@ -4,7 +4,7 @@
     right: 0.5rem;
 
     @media (orientation: landscape) {
-        right: 0.5rem;
+        right: 1rem;
         bottom: 0.5rem;
         top: auto;
     }