Rewrite cPanel deploy guide for the full system (MySQL + frontend)

The guide only covered the API on SQLite. Expand it to the whole
Ardor system on one cPanel account with subdomains:

- Part A (API, app. subdomain): switch to MySQL to match dev — DB
  creation, MySQL .env, permissions for media/experts and
  private/uploads, upload PHP limits, admin, caching, cron.
- Part B (frontend, apex domain): build the static Astro site, set
  PUBLIC_API_URL before building, upload dist/, rebuild after expert
  changes.
- Part C: CORS/cookie/cross-subdomain media wiring, a full-system
  verification checklist (incl. photo change and prescription
  upload/download), MySQL backups, and an updated troubleshooting table.

Uses a YOURDOMAIN placeholder and flags the repo's mismatched domains
to set before deploying.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
