feat: enhance booking flow with BPF wizard, weekend pricing, and document uploads

- Updated translations for German and English to reflect changes in deposit terminology.
- Modified index.html to implement a new booking flow with a step-by-step wizard for vehicle selection, contact details, and ID verification.
- Added CSS styles for the new booking flow interface, including responsive design and improved input styles.
- Created new database policies and tables for handling customer and lead attachments during the booking process.
- Introduced weekend pricing and daily KM limits for vehicles in the database schema.
- Implemented email-based customer upsert functionality to streamline lead qualification and attachment transfer.

Co-authored-by: Copilot <copilot@github.com>

supabase/migrations/post-boot.sql

@@ -83,3 +83,32 @@ create policy "vehicle_photos_admin_update"
 create policy "vehicle_photos_admin_delete"
     on storage.objects for delete to authenticated
     using (bucket_id = 'vehicle-photos');
+
+-- -----------------------------------------------------------------------------
+-- Private bucket for booking documents (ID, payslip)
+-- -----------------------------------------------------------------------------
+insert into storage.buckets (id, name, public, file_size_limit, allowed_mime_types)
+values ('customer-documents','customer-documents', false, 10485760,
+        array['image/jpeg','image/png','application/pdf'])
+on conflict (id) do update
+    set public             = excluded.public,
+        file_size_limit    = excluded.file_size_limit,
+        allowed_mime_types = excluded.allowed_mime_types;
+
+drop policy if exists "custdocs_anon_upload"    on storage.objects;
+drop policy if exists "custdocs_admin_read"     on storage.objects;
+drop policy if exists "custdocs_admin_delete"   on storage.objects;
+
+-- Anon can upload during booking flow
+create policy "custdocs_anon_upload"
+    on storage.objects for insert to anon
+    with check (bucket_id = 'customer-documents');
+
+-- Only authenticated admins can read/delete
+create policy "custdocs_admin_read"
+    on storage.objects for select to authenticated
+    using (bucket_id = 'customer-documents');
+
+create policy "custdocs_admin_delete"
+    on storage.objects for delete to authenticated
+    using (bucket_id = 'customer-documents');