Add Booking module: model, create/read/cancel API, Filament resource (T4.1-T4.7)

- Booking model with booking_vehicle_options line items (supports mixing
  vehicle options like front_seat + back_seat in one booking), price
  snapshot, status machine, and driver/car assignment fields
- BookingService: front-seat max, disabled-option toggles, duplicate-option
  and whole-vehicle-exclusivity guards
- CreateBookingAction, CancelBookingAction, AssignDriverAction
- BookingRefGenerator: sequential EVB-AAAAA1-style refs via row lock
- POST/GET/cancel booking API endpoints (Sanctum, ownership + admin policy)
- BookingPlugin + Filament BookingResource: list, detail view, Cancel and
  Assign Driver actions (shared between table and detail page)
- domain.md updated for multi-vehicle-option bookings (§2) and driver/
  vehicle assignment (§5a)

app-modules/booking/src/Services/BookingRefGenerator.php

@@ -0,0 +1,60 @@
+<?php
+
+namespace Modules\Booking\Services;
+
+use Modules\Booking\Models\Booking;
+
+class BookingRefGenerator
+{
+    private const PREFIX = 'EVB';
+
+    private const CHARS = '123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ';
+
+    /**
+     * Must be called inside the same DB::transaction() as the booking insert
+     * — the row lock on the latest booking is what keeps concurrent callers
+     * from generating the same ref, and it only holds for the transaction's
+     * lifetime.
+     */
+    public function generate(): string
+    {
+        // Lock the latest row so concurrent transactions can't read the same ref.
+        $latest = Booking::lockForUpdate()->orderByDesc('id')->value('booking_ref');
+
+        // If the latest ref doesn't match the expected format, start the sequence fresh.
+        if ($latest && preg_match('/^[A-Z]+-[A-Z0-9]+$/', $latest)) {
+            return $this->incrementRef($latest);
+        }
+
+        return self::PREFIX.'-AAAAA1';
+    }
+
+    private function incrementRef(string $ref): string
+    {
+        preg_match('/^(.*)-([A-Z0-9]+)$/', $ref, $matches);
+
+        $prefix = $matches[1];
+        $suffix = str_split($matches[2]);
+        $base = strlen(self::CHARS);
+        $i = count($suffix) - 1;
+        $carry = true;
+
+        while ($i >= 0 && $carry) {
+            $idx = strpos(self::CHARS, $suffix[$i]);
+
+            if ($idx + 1 < $base) {
+                $suffix[$i] = self::CHARS[$idx + 1];
+                $carry = false;
+            } else {
+                $suffix[$i] = self::CHARS[0];
+            }
+            $i--;
+        }
+
+        if ($carry) {
+            array_unshift($suffix, self::CHARS[0]);
+        }
+
+        return $prefix.'-'.implode('', $suffix);
+    }
+}

app-modules/booking/src/Services/BookingService.php

@@ -0,0 +1,68 @@
+<?php
+
+namespace Modules\Booking\Services;
+
+use Modules\Booking\Data\VehicleSelectionData;
+use Modules\Booking\Exceptions\InvalidVehicleSelectionException;
+use Modules\Shared\Enums\VehicleOption;
+
+class BookingService
+{
+    /**
+     * Enforces the only v1 inventory rule (max Front Seats per booking), the
+     * blunt config toggles for Back Seat / Whole Vehicle availability, and
+     * shape rules around combining options in one booking (no duplicate
+     * option lines, Whole Vehicle can't be mixed with anything else since it
+     * already covers the whole car).
+     *
+     * Deliberately does not check real capacity/availability — that's an
+     * explicitly deferred future phase (domain.md §2, §7).
+     *
+     * @param  list<VehicleSelectionData>  $selections
+     *
+     * @throws InvalidVehicleSelectionException
+     */
+    public function validateSelections(array $selections): void
+    {
+        $seen = [];
+
+        foreach ($selections as $selection) {
+            if (isset($seen[$selection->vehicleOption->value])) {
+                throw InvalidVehicleSelectionException::duplicateOption($selection->vehicleOption);
+            }
+
+            $seen[$selection->vehicleOption->value] = true;
+
+            $this->validateOption($selection->vehicleOption, $selection->passengerCount);
+        }
+
+        if (isset($seen[VehicleOption::WholeVehicle->value]) && count($seen) > 1) {
+            throw InvalidVehicleSelectionException::wholeVehicleCannotBeCombined();
+        }
+    }
+
+    private function validateOption(VehicleOption $vehicleOption, int $passengerCount): void
+    {
+        match ($vehicleOption) {
+            VehicleOption::FrontSeat => $this->validateFrontSeat($passengerCount),
+            VehicleOption::BackSeat => $this->validateEnabled($vehicleOption, 'booking.back_seat_enabled'),
+            VehicleOption::WholeVehicle => $this->validateEnabled($vehicleOption, 'booking.whole_vehicle_enabled'),
+        };
+    }
+
+    private function validateFrontSeat(int $passengerCount): void
+    {
+        $max = config('booking.front_seat_max_per_booking');
+
+        if ($passengerCount > $max) {
+            throw InvalidVehicleSelectionException::frontSeatLimitExceeded($passengerCount, $max);
+        }
+    }
+
+    private function validateEnabled(VehicleOption $vehicleOption, string $configKey): void
+    {
+        if (! config($configKey)) {
+            throw InvalidVehicleSelectionException::optionDisabled($vehicleOption);
+        }
+    }
+}