Add assignment engine, FCM, WebSockets, city gate, and internal APIs

- internal/assignment: GEORADIUS miler assignment with retry/escalation,
  customer-side provider scoring, FCM notifications on assign
- internal/notify: Firebase Admin SDK (FCM) client initialisation
- internal/ws: WebSocket handlers for live parcel tracking and
  customer↔miler chat
- middlewares: city gate (pincode prefix validation), internal API key
  auth, WebSocket JWT auth
- controllers: InternalNotify + InternalReassign for machine-to-machine
  calls; pricing helpers wired into CreateCustomerBooking and CreateCRMBooking
- routes: /internal/*, /ws/bookings/:id/track, /ws/bookings/:id/chat
- models/users, models/doormile_pricing: new fields for device tokens,
  assignment state, pricing bands
- seed_data.sql: initial pricing seed rows

.env and Firebase service-account JSON intentionally excluded.

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

internal/assignment/notify.go

@@ -0,0 +1,55 @@
+package assignment
+
+import (
+	"fmt"
+	"strconv"
+
+	"doormile/db"
+	"doormile/internal/notify"
+	"doormile/models"
+	"doormile/utils"
+)
+
+// notifyMilerNewAssignment sends an FCM push to the miler when a booking is assigned.
+// Non-fatal: failure is logged but never blocks the assignment flow.
+func notifyMilerNewAssignment(profile models.MilerProfile, bookingID int) {
+	if profile.Devicetoken == "" {
+		return
+	}
+	if err := notify.SendToDevice(
+		profile.Devicetoken,
+		"New Pickup Assigned",
+		"New booking assigned — tap to view details",
+		map[string]string{"booking_id": strconv.Itoa(bookingID)},
+	); err != nil {
+		utils.Warn("FCM: failed to notify miler on assignment",
+			"miler_id", profile.Userid,
+			"booking_id", bookingID,
+			"error", err,
+		)
+	}
+}
+
+// notifyCustomerMilerAssigned sends an FCM push to the customer when their miler is assigned.
+// Loads the customer's device token from DB. Non-fatal on any failure.
+func notifyCustomerMilerAssigned(booking *models.PickupBooking, milerName string) {
+	var customer models.AppCustomer
+	if err := db.DB.Where("appcustomerid = ?", booking.Appcustomerid).First(&customer).Error; err != nil {
+		return
+	}
+	if customer.Devicetoken == "" {
+		return
+	}
+	if err := notify.SendToDevice(
+		customer.Devicetoken,
+		"Miler Assigned",
+		fmt.Sprintf("Miler assigned — %s is on the way", milerName),
+		map[string]string{"booking_id": strconv.Itoa(booking.Bookingid)},
+	); err != nil {
+		utils.Warn("FCM: failed to notify customer on assignment",
+			"customer_id", booking.Appcustomerid,
+			"booking_id", booking.Bookingid,
+			"error", err,
+		)
+	}
+}