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/functional_tests/test_navbar.py

@@ -113,7 +113,7 @@ class NavbarByeTest(FunctionalTest):
 class NavbarContGameTest(FunctionalTest):
     """
     When the authenticated user has at least one room with a game event the
-    CONT GAME btn-primary btn-xl appears in the navbar and navigates to that
+    CONT GAME btn-primary appears in the navbar and navigates to that
     room on confirmation.  Its tooltip must also appear below the button.
     """
 
@@ -139,7 +139,6 @@ class NavbarContGameTest(FunctionalTest):
         )
         btn = self.browser.find_element(By.ID, "id_cont_game")
         self.assertIn("btn-primary", btn.get_attribute("class"))
-        self.assertIn("btn-xl", btn.get_attribute("class"))
 
     # ------------------------------------------------------------------ #
     # T6 — CONT GAME tooltip appears below btn                            #