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>

frontend/admin.js

@@ -228,6 +228,8 @@ function loadForEdit(id) {
     vehicleForm.acceleration.value     = v.acceleration;
     vehicleForm.seats.value            = v.seats;
     vehicleForm.daily_price_eur.value  = v.daily_price_eur;
+    vehicleForm.weekend_price_eur.value = v.weekend_price_eur || 0;
+    vehicleForm.max_daily_km.value     = v.max_daily_km || 150;
     vehicleForm.sort_order.value       = v.sort_order;
     vehicleForm.location.value         = v.location;
     vehicleForm.description_de.value   = v.description_de;
@@ -246,6 +248,8 @@ resetBtn.addEventListener("click", () => {
     vehicleForm.sort_order.value = 100;
     vehicleForm.location.value = "Steiermark (TBD)";
     vehicleForm.seats.value = 2;
+    vehicleForm.max_daily_km.value = 150;
+    vehicleForm.weekend_price_eur.value = 0;
     state.currentPhotoPath = null;
     updatePreview("");
     formTitle.textContent = "Neues Fahrzeug";
@@ -267,6 +271,8 @@ vehicleForm.addEventListener("submit", async (e) => {
             acceleration:    fd.get("acceleration") || "",
             seats:           +fd.get("seats") || 2,
             daily_price_eur: +fd.get("daily_price_eur") || 0,
+            weekend_price_eur: +fd.get("weekend_price_eur") || 0,
+            max_daily_km:    +fd.get("max_daily_km") || 150,
             sort_order:      +fd.get("sort_order") || 100,
             location:        fd.get("location") || "Steiermark (TBD)",
             description_de:  fd.get("description_de") || "",