Private session messages now follow your wording — and can text and push

Private sessions had quietly been the exception. Every other automated message
picks up your logo, your footer and any wording you'd written for it — the
private-session confirmation did not, because it was assembled as plain text
outside the normal email design. Anything you typed for it simply never
appeared.

That's fixed. From now on:

- **The confirmation and the reminders look like your venue** — your logo,
  your colours, your footer and links on your own web address (or your brand's,
  when the enquiry came through a brand page). The calendar invite is still
  attached exactly as before.
- **Your wording is used.** Whatever you've written for these events in
  Settings → Emails now shows at the top of the message, above the session
  details. The details, times and buttons stay in place, so a reword can never
  accidentally remove the information a client needs.
- **You can switch them on or off.** The private-session confirmation and
  reminder now appear in Settings → Emails → Events like every other message.
- **You can also text and push them.** Both go out by SMS and as a phone
  notification when you want them to, with the wording editable in Settings →
  Emails → Text messages. Each channel has its own switch, so you can text the
  reminder without texting the confirmation.
- **The "you've been assigned a private session" notice for your instructor is
  now a real setting.** It had been sending for a long time without appearing
  anywhere you could see it. It now has its own row in Events settings, its own
  wording, and a phone notification for the instructor.