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/sr.json

@@ -754,6 +754,7 @@
 			"termsAccept": "I am 18+ and accept the {hotel} terms & rules.",
 			"createAccount": "Креирајте налог",
 			"creatingAccount": "Прављење налога...",
+			"redirecting": "Преусмеравање на ваш налог...",
 			"alreadyHaveAccount": "Већ имате налог? Пријавите се!",
 			"register": "Региструјте се",
 			"termsError": "Морате прихватити услове и правила да бисте се регистровали.",