Multi-backend support

Squashed commit of the following:

commit 92518024ba295456358618c0e8180bd8e996fdf1
Author: Birte Kristina Friesel <birte.friesel@uos.de>
Date:   Fri Jul 26 18:39:46 2024 +0200

    add_or_update station: remove superfluos 'new backend id := old backend id'

commit df21c20c6e4c86454f8a9ac69121404415217f2a
Author: Birte Kristina Friesel <birte.friesel@uos.de>
Date:   Fri Jul 26 18:35:51 2024 +0200

    revert connection targets min_count to 3

commit be335cef07d0b42874f5fc1de4a1d13396e8e807
Author: Birte Kristina Friesel <birte.friesel@uos.de>
Date:   Fri Jul 26 18:20:05 2024 +0200

    mention backend selection in API documentation

commit 9f41828fb4f18fd707e0087def3032e8d4c8d7d8
Author: Birte Kristina Friesel <derf@finalrewind.org>
Date:   Thu Jul 25 20:19:23 2024 +0200

    use_history: not all backends provide route data in departure monitor

commit 09714b4d89684b8331d0e96f564a4c7432318f70
Author: Birte Kristina Friesel <derf@finalrewind.org>
Date:   Thu Jul 25 20:11:44 2024 +0200

    disambiguation: pass correct hafas parameter

commit 8cdf1120fc32155dc6525be64601b7c10a9c7f52
Author: Birte Kristina Friesel <derf@finalrewind.org>
Date:   Thu Jul 25 20:11:28 2024 +0200

    _checked_in: hide Zuglauf link for non-db checkins

commit 7455653f541198e0e0a6d11aed421487ffdb6285
Author: Birte Kristina Friesel <derf@finalrewind.org>
Date:   Thu Jul 25 20:01:47 2024 +0200

    debug output

commit b9cda07f85601a58ea32dbdacdd5399f302db52b
Author: Birte Kristina Friesel <derf@finalrewind.org>
Date:   Thu Jul 25 19:09:07 2024 +0200

    fix remaining get_connection_targets / get_connecting_trains_p invocations

commit 2759d7258c37c7498905cfe19f6b4c4f6d16bd21
Author: Birte Kristina Friesel <derf@finalrewind.org>
Date:   Wed Jul 24 20:50:12 2024 +0200

    support non-DB HAFAS backends (WiP)

1 files changed, 46 insertions, 0 deletions

diff --git a/lib/Travelynx/Controller/Account.pm b/lib/Travelynx/Controller/Account.pm
index 5c101b1..b7b2b78 100644
--- a/lib/Travelynx/Controller/Account.pm
+++ b/lib/Travelynx/Controller/Account.pm
@@ -999,6 +999,52 @@ sub password_form {
 	$self->render('change_password');
 }
 
+sub backend_form {
+	my ($self) = @_;
+	my $user = $self->current_user;
+
+	my @backends = $self->stations->get_backends;
+
+	for my $backend (@backends) {
+		my $type = 'UNKNOWN';
+		if ( $backend->{iris} ) {
+			$type = 'IRIS-TTS';
+			$backend->{name} = 'DB';
+		}
+		elsif ( $backend->{hafas} ) {
+			$type = 'HAFAS';
+			$backend->{longname}
+			  = $self->hafas->get_service( $backend->{name} )->{name};
+		}
+		$backend->{type} = $type;
+	}
+
+	$self->render(
+		'select_backend',
+		backends    => \@backends,
+		user        => $user,
+		redirect_to => $self->req->param('redirect_to') // '/',
+	);
+}
+
+sub change_backend {
+	my ($self) = @_;
+
+	my $backend_id = $self->req->param('backend');
+	my $redir      = $self->req->param('redirect_to') // '/';
+
+	if ( $backend_id !~ m{ ^ \d+ $ }x ) {
+		$self->redirect_to($redir);
+	}
+
+	$self->users->set_backend(
+		uid        => $self->current_user->{id},
+		backend_id => $backend_id,
+	);
+
+	$self->redirect_to($redir);
+}
+
 sub change_password {
 	my ($self)       = @_;
 	my $old_password = $self->req->param('oldpw');