feat: add Projects settings with sub-locations and cascading dropdowns in purchase request modal

- Migration: add project_id FK to settings_locations
- Models: ProjectSetting hasMany Location, Location belongsTo ProjectSetting
- Settings: /settings/projects page — manage projects and their sub-locations (two-panel UI)
- Sidebar: Projects nav item under Settings group
- Routes: 7 new settings/projects routes (Admin only)
- Modal: project_name and location fields now cascading dropdowns populated from settings_projects/settings_locations

Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

app/Models/Settings/Location.php

@@ -8,7 +8,7 @@ class Location extends Model
 {
     protected $table = 'settings_locations';
 
-    protected $fillable = ['name', 'is_active'];
+    protected $fillable = ['name', 'project_id', 'is_active'];
 
     protected $casts = ['is_active' => 'boolean'];
 
@@ -16,4 +16,9 @@ class Location extends Model
     {
         return $query->where('is_active', true);
     }
+
+    public function project(): \Illuminate\Database\Eloquent\Relations\BelongsTo
+    {
+        return $this->belongsTo(\App\Models\Settings\ProjectSetting::class, 'project_id');
+    }
 }

app/Models/Settings/ProjectSetting.php

@@ -16,4 +16,9 @@ class ProjectSetting extends Model
     {
         return $query->where('is_active', true);
     }
+
+    public function locations(): \Illuminate\Database\Eloquent\Relations\HasMany
+    {
+        return $this->hasMany(\App\Models\Settings\Location::class, 'project_id');
+    }
 }