feat: add nerve to stats bar, gym nav link, nerve dashboard card

- Add nerve chip to stats-bar showing current/max nerve with purple brain icon
- Add Gym link to sidebar navigation with muscle emoji and active state
- Add Nerve card to dashboard with progress bar, description, and Go to Gym link

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

resources/views/game/partials/stats-bar.blade.php

@@ -12,6 +12,12 @@
         <span class="text-gray-300">{{ $character->energy }}<span class="text-gray-600">/{{ $character->max_energy }}</span></span>
     </div>
 
+    {{-- Nerve --}}
+    <div class="flex items-center space-x-1 bg-syndicate-800 border border-syndicate-700 rounded px-2 py-1">
+        <span class="text-purple-400">🧠</span>
+        <span class="text-gray-300">{{ $character->nerve }}<span class="text-gray-600">/{{ $character->max_nerve }}</span></span>
+    </div>
+
     {{-- Cash --}}
     <div class="flex items-center space-x-1 bg-syndicate-800 border border-syndicate-700 rounded px-2 py-1">
         <span class="text-gold-400">$</span>