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>

main.go

@@ -9,6 +9,7 @@ import (
 	"doormile/config"
 	"doormile/controllers"
 	"doormile/db"
+	"doormile/internal/notify"
 	"doormile/internal/worker"
 	"doormile/middlewares"
 	"doormile/migrations"
@@ -31,6 +32,7 @@ func main() {
 	db.Connect(cfg)
 	db.InitRedis(cfg)
 	db.InitNATS(cfg)
+	notify.InitFCM()
 
 	// 3. Run GORM migrations for logistics tables
 	if db.DB != nil {