Add massage as a third vertical, driven by a config registry

Introduces /massage alongside barber and beauty: landing page, booking
flow, admin support, home tile and SEO entries, in all three languages.

Architecture
- application/config/verticals.php + vertical_helper.php: one registry
  entry per vertical (branding, assets, views, behaviour flags). A fourth
  vertical is a config entry plus content files.
- Strangler: barber and beauty keep pointing at their existing view files,
  so their rendered HTML is unchanged. Only massage uses the new generic
  pages/vertical-*.php and includes/vertical-*.php views, which collapse
  the four duplicated per-language nav/footer branches into one.
- Pages::vertical() + one route; booking(), booking_finished(),
  _booking_error() and manage_booking() are now registry-driven.

Worker/vertical coupling
- getActiveWorkers() derives the vertical from services.service_category_id
  instead of the workers.is_barber / is_beauty flags, which were a
  hand-maintained cache of exactly that fact. Verified against production
  data: the derived set reproduced the stored flags for every worker, in
  both verticals. No schema change was needed for massage.
- The legacy flags are now written through from the category so a rollback
  cannot strand a new worker, and the admin worker UI shows the derived
  verticals read-only instead of two dropdowns that controlled nothing.

Bug fixes found along the way (all pre-existing)
- booking_process() had no server-side category guard; cross-vertical
  mixing was prevented only by client-side JS.
- add-service-form / add-worker-form emitted `selected` on every category
  option, so the newest category silently became the default.
- update-service-form offered only barber/beauty, so editing a service of
  any other type silently rewrote it.
- getWorkerScheduleByDay ignored schedule overrides while getAvailableTimes
  honoured them, so slots could be shown and then rejected. Added an
  override-aware getWorkerScheduleForDate() and used it in both guards.
- Booking lists dereferenced a null service if one had been hard-deleted.
- main.css: .tiles was tuned for exactly two tiles, including an
  absolutely-positioned .style1 at the 1280px breakpoint.

Massage-specific behaviour, opt-in per vertical
- strip_category_prefix: grouped service lists show "50 min" under the
  treatment heading rather than repeating the full name. The full name is
  carried in data-service-name so the totals panel stays unambiguous, and
  services.service_name is untouched for emails and admin.
- single_service_booking: one treatment per booking, enforced in the UI and
  in booking_process(). Re-clicking the selection releases it.
- Displayed treatment time (50/80/110 min) is in the service name; the
  booked slot (60/90/120 min) is service_time and covers changing and
  payment. service_time is never shown to the guest.

DB migrations for dev/prod are in documents/ - additive only, no ALTER.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

application/views/pages/manage-booking-cancelled.php

@@ -7,11 +7,11 @@
         if($firstService) $subpage = $firstService->service_type;
     }
 
-    if($subpage == 'beauty'){
-        include(getcwd().'/application/views/includes/beauty-skeleton-top.php');
-    } else {
-        include(getcwd().'/application/views/includes/barber-skeleton-top.php');
+    $vertical = vertical_get($subpage);
+    if(!$vertical){
+        $vertical = vertical_get('barber');
     }
+    include(getcwd().'/application/views/includes/'.$vertical['skeleton'].'-skeleton-top.php');
 
     $messages = array(
         'no' => 'Din bestilling den <strong>'.$booking->booking_date.'</strong> kl. <strong>'.date('H:i', strtotime($booking->booking_start_time)).'</strong> med <strong>'.htmlspecialchars($worker->worker_name, ENT_QUOTES, 'UTF-8').'</strong> er avbestilt.',
@@ -36,9 +36,5 @@
 </div>
 
 <?php
-    if($subpage == 'beauty'){
-        include(getcwd().'/application/views/includes/beauty-skeleton-bottom.php');
-    } else {
-        include(getcwd().'/application/views/includes/barber-skeleton-bottom.php');
-    }
+    include(getcwd().'/application/views/includes/'.$vertical['skeleton'].'-skeleton-bottom.php');
 ?>