feat(snake): add Snake mini-game tab with pause, bonus food, and skin palettes

- New Snake game as 4th tab with canvas rendering and game loop
- Snake engine: pure functions for grid movement, collision, scoring
- Bonus food: gold diamonds spawn randomly for +25pts +2 growth
- Pause overlay: shows PAUSED + score when leaving tab mid-game
- Skin palettes: 6 retro color schemes (Auto/Green/Olive/Amber/Grey/Rose)
  cycle with P key, persisted in localStorage, Auto reads CSS theme var
- High score persistence across sessions, speed ramp as score increases
- Directional eyes on snake head, food chime, game-over sound
- Footer hides on Snake tab to maximize game area
- D-pad controls snake; Left/Right do NOT switch tabs while playing
- Power switch disabled on Snake tab to avoid P key conflict
- 24 unit tests (engine) + 4 e2e tests (Chromium/Firefox/WebKit)
- 48/48 e2e passing, 51/51 unit tests passing

Author: swapsha96

src/components/GameBoy.astro

@@ -8,6 +8,7 @@ import TurnButton from './gameboy/TurnButton.astro';
 import LinksTab from './gameboy/tabs/LinksTab.astro';
 import AboutTab from './gameboy/tabs/AboutTab.astro';
 import HelpTab from './gameboy/tabs/HelpTab.astro';
+import SnakeTab from './gameboy/tabs/SnakeTab.astro';
 import '../styles/hit-areas.css';
 import '../styles/console-layout.css';
 import '../styles/view-transitions.css';
@@ -62,6 +63,9 @@ const aboutText = aboutEntry && aboutEntry.body ? aboutEntry.body.trim() : '';
                     <div class="tab-content" id="tab-2" role="tabpanel" aria-labelledby="tab-ind-2" hidden>
                         <HelpTab />
                     </div>
+                    <div class="tab-content" id="tab-3" role="tabpanel" aria-labelledby="tab-ind-3" hidden>
+                        <SnakeTab />
+                    </div>
                 </div>
 
                 <footer class="footer">

src/components/gameboy/TabsHeader.astro

@@ -2,4 +2,5 @@
   <button type="button" class="tab-indicator active" id="tab-ind-0" role="tab" aria-selected="true" aria-controls="tab-0">LINKS</button>
   <button type="button" class="tab-indicator" id="tab-ind-1" role="tab" aria-selected="false" aria-controls="tab-1">ABOUT</button>
   <button type="button" class="tab-indicator" id="tab-ind-2" role="tab" aria-selected="false" aria-controls="tab-2">HELP</button>
+  <button type="button" class="tab-indicator" id="tab-ind-3" role="tab" aria-selected="false" aria-controls="tab-3">SNAKE</button>
 </div>