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>

app/Models/Crime.php

@@ -19,6 +19,7 @@ use Illuminate\Database\Eloquent\Relations\HasMany;
  * @property int $reward_max
  * @property int $experience
  * @property int $energy_cost
+ * @property int $nerve_cost
  * @property int $cooldown
  * @property int|null $requires_level
  * @property int|null $location_id
@@ -39,6 +40,7 @@ class Crime extends Model
         'reward_max',
         'experience',
         'energy_cost',
+        'nerve_cost',
         'cooldown',
         'requires_level',
         'location_id',