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/de.json

@@ -724,6 +724,7 @@
 			"termsAccept": "Ich bin 18+ und akzeptiere die {hotel} AGB & Regeln.",
 			"createAccount": "Konto erstellen",
 			"creatingAccount": "Konto wird erstellt...",
+			"redirecting": "Weiterleitung zu deinem Account...",
 			"alreadyHaveAccount": "Bereits ein Konto? Anmelden!",
 			"register": "Registrieren",
 			"termsError": "Du musst die AGB & Regeln akzeptieren, um dich zu registrieren.",