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/templates/apps/gameboard/_partials/_gatekeeper.html

@@ -53,7 +53,7 @@
                     {% if room.gate_status == 'OPEN' %}
                         <form method="POST" action="{% url 'epic:pick_roles' room.id %}" style="display:contents">
                             {% csrf_token %}
-                            <button type="submit" class="launch-game-btn btn btn-primary btn-xl">PICK ROLES</button>
+                            <button type="submit" class="launch-game-btn btn btn-primary">PICK ROLES</button>
                         </form>
                     {% endif %}
                 </div>

src/templates/apps/gameboard/_partials/_table_positions.html

@@ -8,7 +8,7 @@
                 <form method="POST" action="{% url 'epic:confirm_token' room.id %}">
                     {% csrf_token %}
                     {% if is_last_slot %}
-                        <button type="submit" class="btn btn-primary btn-xl">PICK ROLES</button>
+                        <button type="submit" class="btn btn-primary">PICK ROLES</button>
                     {% else %}
                         <button type="submit" class="btn btn-confirm">OK</button>
                     {% endif %}

src/templates/apps/gameboard/room.html

@@ -14,7 +14,7 @@
                 <div id="id_pick_sigs_wrap"{% if starter_roles|length < 6 %} style="display:none"{% endif %}>
                     <form method="POST" action="{% url 'epic:pick_sigs' room.id %}">
                         {% csrf_token %}
-                        <button id="id_pick_sigs_btn" type="submit" class="btn btn-primary btn-xl">PICK<br>SIGS</button>
+                        <button id="id_pick_sigs_btn" type="submit" class="btn btn-primary">PICK<br>SIGS</button>
                     </form>
                 </div>
                 {% endif %}