Fix 9 backend bugs: pricing, zones, geocoding, device tokens, assignment retry

- pricingid null: lookupDoormilePrice now returns matched rule ID; wired to BookingServiceOption.Pricingid
- Zone rename: Interstate→Regional, OtherState→National throughout (code + DB migrated)
- Zone from pincodes: CheckPrice now accepts pickup_pincode+delivery_pincode and auto-resolves zone
- Delivery geocoding: pincodeToLatLon() maps 3-digit prefix to city coords when lat/lon are 0
- Device tokens: device_token field added to PinVerify DTOs; saved on both customer and miler login
- Assignment retry: RejectMilerAssignment now re-triggers AssignCustomerMiler/AssignCRMMiler immediately
- Provider empty B2C: defaults to Doormile when no pricing provider row matches
- City gate 422→400: StatusUnprocessableEntity corrected to StatusBadRequest
- Miler GPS 0,0: WS tracking falls back to MilerProfile DB coords when Redis key is expired

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

internal/assignment/customer_assignment.go

@@ -105,12 +105,12 @@ func tryCustomerAssign(bookingID int) (bool, error) {
 
 	provider, providerFound := selectBestProvider(zone, category, serviceType, weight)
 	if !providerFound {
-		utils.Warn("B2CAssignment: no provider pricing match, proceeding without one",
+		utils.Warn("B2CAssignment: no provider pricing match, defaulting to Doormile",
 			"booking_id", bookingID,
 			"zone", zone,
 			"category", category,
 		)
-		provider = providerResult{}
+		provider = providerResult{company: "Doormile"}
 	}
 
 	// Step 6 — ETA based on miler-to-pickup distance.
@@ -359,9 +359,9 @@ func b2cResolveZone(pickupPincode, deliveryPincode string) string {
 		return "Local"
 	}
 	if b2cPincodeToState(pickupPincode) == b2cPincodeToState(deliveryPincode) {
-		return "Interstate"
+		return "Regional"
 	}
-	return "OtherState"
+	return "National"
 }
 
 func b2cNormalizePricingCategory(category string) string {