Phase 3 testing fixes: Fastify 5, SSE→WebSocket+FCM, enums, security, session lifecycle

- Upgrade Fastify 4→5 with all plugins (@fastify/websocket 11, cors 11, sensible 6)
- Migrate all SSE endpoints to WebSocket + FCM push (mitra chat requests, customer pairing status)
- Add flutter_local_notifications for foreground push notifications with sound
- Add splash screen to both apps (hide auth loading flash)
- Introduce constants/enums across entire codebase (no raw string literals)
- Move price tiers from hardcoded array to app_config DB (data-driven, includes 1-min test tier)
- Add session ownership validation on all shared chat routes
- Add ownership checks on endSession, respondToExtension, requestExtension
- Fix session timer: auto-complete expired/stale sessions on server restart
- Add 5-min grace period for abandoned closing sessions
- Fix extension flow: proper session_resumed handling, clearExtensionRequest, closure grace timer cleanup
- Fix chat screens: ConnectChat in initState, session status check on connect
- Fix customer expired view: 5-min countdown, closure state priority over expired state
- Fix mitra extension UI: loading spinner, disable buttons, handle EXTENSION_RESOLVED error
- Fix GoRouter navigation consistency (no more Navigator.pushNamed)
- Fix goodbye view keyboard overflow (SingleChildScrollView)
- Add active session card on customer home screen with refresh on navigate back
- Fix PricingBottomSheet extension mode (RequestExtension instead of new pairing)
- Send session_resumed to both parties on extension accept

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/src/constants.js

@@ -0,0 +1,101 @@
+// User types
+export const UserType = Object.freeze({
+  CUSTOMER: 'customer',
+  MITRA: 'mitra',
+})
+
+// Chat session statuses
+export const SessionStatus = Object.freeze({
+  SEARCHING: 'searching',
+  PENDING_ACCEPTANCE: 'pending_acceptance',
+  PENDING_PAYMENT: 'pending_payment',
+  ACTIVE: 'active',
+  EXTENDING: 'extending',
+  CLOSING: 'closing',
+  COMPLETED: 'completed',
+  CANCELLED: 'cancelled',
+  EXPIRED: 'expired',
+})
+
+// Chat message statuses
+export const MessageStatus = Object.freeze({
+  SENT: 'sent',
+  DELIVERED: 'delivered',
+  READ: 'read',
+})
+
+// Chat message types
+export const MessageType = Object.freeze({
+  TEXT: 'text',
+})
+
+// Chat request notification responses
+export const NotificationResponse = Object.freeze({
+  ACCEPTED: 'accepted',
+  DECLINED: 'declined',
+  IGNORED: 'ignored',
+})
+
+// Session extension statuses
+export const ExtensionStatus = Object.freeze({
+  PENDING: 'pending',
+  ACCEPTED: 'accepted',
+  REJECTED: 'rejected',
+  TIMEOUT: 'timeout',
+})
+
+// Customer transaction types
+export const TransactionType = Object.freeze({
+  FREE_TRIAL: 'free_trial',
+  PAID: 'paid',
+  EXTENSION: 'extension',
+})
+
+// Who ended a session
+export const EndedBy = Object.freeze({
+  SYSTEM: 'system',
+  CUSTOMER: 'customer',
+  MITRA: 'mitra',
+})
+
+// WebSocket message types
+export const WsMessage = Object.freeze({
+  // Auth
+  AUTH: 'auth',
+  AUTH_OK: 'auth_ok',
+  ERROR: 'error',
+
+  // Chat
+  MESSAGE: 'message',
+  MESSAGE_ACK: 'message_ack',
+  MESSAGE_STATUS: 'message_status',
+  TYPING: 'typing',
+
+  // Pairing
+  CHAT_REQUEST: 'chat_request',
+  CHAT_REQUEST_CLOSED: 'chat_request_closed',
+  PAIRED: 'paired',
+
+  // Session lifecycle
+  SESSION_TIMER: 'session_timer',
+  SESSION_EXPIRED: 'session_expired',
+  SESSION_CLOSING: 'session_closing',
+  SESSION_COMPLETED: 'session_completed',
+  SESSION_ENDED: 'session_ended',
+  SESSION_PAUSED: 'session_paused',
+  SESSION_RESUMED: 'session_resumed',
+  SESSION_ASSIGNED: 'session_assigned',
+  SESSION_REROUTED: 'session_rerouted',
+  REROUTED: 'rerouted',
+
+  // Extension
+  EXTENSION_REQUEST: 'extension_request',
+  EXTENSION_RESPONSE: 'extension_response',
+
+  // Early end
+  EARLY_END: 'early_end',
+
+  // Delivery
+  DELIVERED: 'delivered',
+  READ: 'read',
+})