feat: add nerve config and Character nerve methods

Add nerve system configuration to config/game.php with start_amount,
max, regen_rate, regen_interval, and midnight_refill settings. Add gym
configuration with energy_cost, daily_cap, and stat_gain. Add nerve
methods to Character model: hasNerve(), consumeNerve(), addNerve(), and
getNervePercentageAttribute(). Update levelUp() to increment max_nerve
by 2. Add nerve_cost to fillable arrays in Crime and CrimeAttempt models.

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

config/game.php

@@ -27,6 +27,7 @@ return [
             'attack' => 15,
             'travel' => 5,
             'train' => 20,
+            'gym' => 20,
         ],
     ],
 
@@ -40,6 +41,22 @@ return [
         'death_threshold' => 0,          // Health <= 0 = dead
     ],
 
+    // Nerve system configuration
+    'nerve' => [
+        'start_amount'   => 100,
+        'max'            => 100,
+        'regen_rate'     => 1,     // nerve per tick
+        'regen_interval' => 300,   // seconds (5 minutes)
+        'midnight_refill' => true,
+    ],
+
+    // Gym training configuration
+    'gym' => [
+        'energy_cost' => 20,
+        'daily_cap'   => 5,        // sessions per stat per day
+        'stat_gain'   => 1,        // stat points per session
+    ],
+
     // Combat system configuration
     'combat' => [
         'base_damage' => 5,