Register: auto sign-in to /me and speed/cleanup improvements

- Send the verification email after the response via after() so it
  never blocks sign-up
- Invalidate the cached login lookup right after account creation so
  the automatic sign-in always finds the fresh row
- Auto sign in with the submitted credentials and go straight to /me,
  with a fallback to /login?registered=1 if sign-in is refused (e.g.
  email verification required)
- Cache the register page's online/latest user queries to cut DB load
  under traffic
- Fix terms checkbox label double-toggle cancelling the selection
- Add pages.register.redirecting translation to all locales

src/messages/nl.json

@@ -907,6 +907,7 @@
 			"termsAccept": "Ik ben 18+ en accepteer de {hotel} voorwaarden & regels.",
 			"createAccount": "Account aanmaken",
 			"creatingAccount": "Account wordt aangemaakt...",
+			"redirecting": "Doorgaan naar je account...",
 			"alreadyHaveAccount": "Al een account? Inloggen!",
 			"register": "Registreren",
 			"alreadyHaveAccountPre": "Al een account?",