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>

middlewares/city_gate.go

@@ -0,0 +1,40 @@
+package middlewares
+
+import (
+	"encoding/json"
+	"strings"
+
+	"github.com/gofiber/fiber/v2"
+)
+
+// operatingCityPrefixes maps supported 3-digit pincode prefixes to city names.
+var operatingCityPrefixes = map[string]string{
+	"641": "Coimbatore",
+	"600": "Chennai",
+	"560": "Bengaluru",
+	"500": "Hyderabad",
+}
+
+// CityGateMiddleware rejects bookings from pincodes outside Doormile's operating cities.
+// It reads pickuppincode from the JSON body without consuming it, so the downstream
+// controller can still call c.BodyParser() as usual.
+func CityGateMiddleware(c *fiber.Ctx) error {
+	var body struct {
+		Pickuppincode string `json:"pickuppincode"`
+	}
+	if err := json.Unmarshal(c.Body(), &body); err != nil || body.Pickuppincode == "" {
+		return c.Next()
+	}
+
+	pincode := strings.TrimSpace(body.Pickuppincode)
+	if len(pincode) >= 3 {
+		if _, ok := operatingCityPrefixes[pincode[:3]]; ok {
+			return c.Next()
+		}
+	}
+
+	return c.Status(fiber.StatusUnprocessableEntity).JSON(fiber.Map{
+		"error": "We are not yet operating in your city. Stay tuned!",
+		"code":  "CITY_NOT_SUPPORTED",
+	})
+}