security: round 1 — quick wins (rate limiting, headers, mass assignment, logging)

- Add throttle middleware to login (5/min), portal/token-auth (10/min),
  volunteer-register (5/min), and invitation routes (10/min)
- Set Sanctum token expiration to 7 days
- Remove billing_status from UpdateOrganisationRequest (super_admin only)
- Revoke all Sanctum tokens on password reset
- Strengthen password rules: min 8 chars, mixed case, numbers
- Create SecurityHeaders middleware (X-Content-Type-Options, X-Frame-Options,
  HSTS, Referrer-Policy, Permissions-Policy)
- Fix open redirect on all 3 login pages (validate ?to= starts with /)
- Set APP_DEBUG=false in .env.example
- Log failed login attempts with email, IP, user-agent
- Log authorization failures (403) with user, IP, path, method
- Harden mass assignment: remove user_id from Person, audit fields from
  ShiftAssignment, system fields from UserInvitation $fillable
- Replace real DB records with factory make() in mail preview routes

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

api/app/Models/UserInvitation.php

@@ -17,13 +17,7 @@ final class UserInvitation extends Model
 
     protected $fillable = [
         'email',
-        'invited_by_user_id',
-        'organisation_id',
         'event_id',
-        'role',
-        'token',
-        'status',
-        'expires_at',
     ];
 
     protected function casts(): array
@@ -60,12 +54,14 @@ final class UserInvitation extends Model
 
     public function markAsAccepted(): void
     {
-        $this->update(['status' => 'accepted']);
+        $this->status = 'accepted';
+        $this->save();
     }
 
     public function markAsExpired(): void
     {
-        $this->update(['status' => 'expired']);
+        $this->status = 'expired';
+        $this->save();
     }
 
     public function scopePending(Builder $query): Builder