Add per-customer booking flow checklist + fix admin login

Admin portal overhaul:
- Fix require_once path (was admin/db.php, should be ../db.php) — this was
  the root cause of the login always redirecting back to the login page
- Fix session save path to /home/parkerslingshotrentals.com/sessions so the
  web user (parke1909) can actually read sessions back (the system default
  /var/lib/php/sessions was write-only for non-root)
- Fix AJAX unauthenticated response: return 401 JSON instead of login HTML
- Fresh bcrypt hash for admin password (Parker2026!)
- Add 3 new DB columns: insurance_verified, deposit_received, license_verified
- Replace flat bookings table with expandable per-customer flow panel:
  click any row to open a 3-column detail drawer showing:
  (1) full contact info + admin notes
  (2) 6-step booking flow checklist with inline toggle buttons for steps
      that admin marks (insurance, deposit, license)
  (3) send-reminder email builder — pick which pending items to include,
      send customer a personalized nudge with waiver link + instructions
- Progress dots in table row update live when admin toggles a step
- Stats row now includes waiver, insurance, deposit counts

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

db.php

@@ -5,7 +5,7 @@ define('PARKER_DB_USER', 'parker_user');
 define('PARKER_DB_PASS', 'Pk4rk3r_2026!Tx');
 
 define('ADMIN_USER', 'admin');
-define('ADMIN_PASS', '$2y$12$Tz8QkXv9mNpL3wR1uE6OaOQbKjH5sYdF2cVnMxPt7lGAeWqZiBSHu'); // Parker2026!
+define('ADMIN_PASS', '$2y$10$ynnk3RfarOD7VIJizC30kuXqu6tQ3gotNrlp5y33afh5fPOgnAMU6'); // Parker2026!
 define('ADMIN_SESSION_KEY', 'parker_admin_auth');
 
 define('SENDGRID_API_KEY', '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');