security: fix unauthenticated file upload/RCE risk, TLS bypass, XSS, and broken gift-card/review columns

- admin/api/upload-splash.php had NO admin-auth check (included the public
  customer header, not admin/includes/header.php) and both upload endpoints
  trusted the client-supplied MIME type and filename extension, so an
  attacker could name a file "shell.php", spoof Content-Type: image/png,
  and get PHP written into a web-reachable uploads/ directory. Added
  AdminAuth check and centralized real-content validation (getimagesize +
  server-side extension mapping) in a new handleImageUpload() helper used
  by both admin/upload-image.php and admin/api/upload-splash.php.
- Removed CURLOPT_SSL_VERIFYPEER => false from the CyberMail email calls
  in includes/email.php and includes/functions.php (MITM risk on the API
  key). Rewrote functions.php's sendEmail() as a thin wrapper around
  Email::send() so there's one implementation instead of two that could
  drift (this is what had the second copy of the TLS bypass).
- Escaped customer-controlled fields (customer_name, tracking info, reset
  URL) before interpolating into outbound HTML emails — name is free text
  from registration/checkout with no length/char restriction, so it was
  stored-HTML-injectable into every transactional email.
- Fixed api/redeem-gift-card.php referencing a nonexistent `balance` column
  on gift_cards (actual column is current_balance) — gift card redemption
  was completely broken, always returning "no remaining balance".
- Fixed api/submit-review.php inserting into nonexistent `content`/`status`
  columns on reviews (actual columns are `comment`/`is_approved`) — review
  submission was crashing on every request.
- Hardened .htaccess: block /db/*, /.git/*, and *.sql. Live site currently
  serves db/schema.sql and the full .git directory (including .git/config,
  which contains a GitHub PAT with push access) over HTTP — the existing
  config/includes RedirectMatch rules are also not being enforced live,
  see report for details; this needs a server-level fix too.
- Cleaned up README's leftover install instructions pointing at a deleted
  create-admin.php with a documented default password.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

README.md

@@ -75,10 +75,10 @@ A complete e-commerce platform built with **PHP 8.4** and **MySQL 8.0** for cPan
    ```
 
 6. **Create Admin User**
-   - Visit: `https://yoursite.com/create-admin.php`
-   - Or import the default admin from schema.sql:
-     - Email: `admin@tomsjavajive.com`
-     - Password: `admin123!`
+   - `create-admin.php` and the seeded default admin account have been removed —
+     insert your own row into `admin_users` directly (via phpMyAdmin/CLI) with a
+     bcrypt hash from `password_hash($password, PASSWORD_BCRYPT, ['cost' => 12])`.
+     Never leave a well-known default password (e.g. `admin123!`) in place.
 
 7. **Configure Site URL**
    - Edit `config/config.php`: