Add profile page for changing password and email

New /profile route (nav link between Admin and Logout) with two
independent forms, both requiring the current password before
applying a change:
- Change password: standard current/new/repeat flow, same password
  strength rules as registration.
- Change email: re-checks the new address isn't already taken (avoids
  a 500 from the unique constraint), then marks the account
  unverified and re-sends the confirmation email via the existing
  EmailVerifier/verify-email flow, same as registration. The current
  session stays logged in, but the user needs to verify the new
  address before their next login (UserChecker already blocks
  unverified accounts).

translations/messages.en.yaml

@@ -3,6 +3,7 @@ site.name: EscapePage
 nav.home: Home
 nav.game: Game
 nav.admin: Admin
+nav.profile: Profile
 nav.login: Login
 nav.register: Register
 nav.logout: Logout

translations/messages.nl.yaml

@@ -3,6 +3,7 @@ site.name: EscapePage
 nav.home: Start
 nav.game: Spel
 nav.admin: Beheer
+nav.profile: Profiel
 nav.login: Inloggen
 nav.register: Registreren
 nav.logout: Uitloggen