docs(app): add real-backend app walkthrough screenshots, PPTX deck, and fix stale LAN IP

Captures the full DO Scan and Product Scan flows end-to-end against the live
backend (real OCR extraction, real DINOv2 product classification, a genuine
network-timeout failure, and a live validation-gap finding) for use in
presentations. WORKFLOW.md documents every screen/button/algorithm, and
Prima-Mart-Scanner-Workflow.pptx turns it into a 23-slide deck.

Also updates AppConfig's hardcoded LAN IP (192.168.70.4 -> 192.168.100.20)
to match the current dev machine's address, discovered while reproducing the
upload flow against the real backend.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01JSgYVUWJTGMk7SZqqHH8xy

lib/config/app_config.dart

@@ -19,7 +19,7 @@ class AppConfig {
   // - Physical Device on same Wi-Fi: use the backend machine's current LAN IP
   // - Android Emulator: use 'http://10.0.2.2:8000/api/v1'
   // - iOS Simulator: use 'http://localhost:8000/api/v1'
-  static const String _lanBaseUrl = 'http://192.168.70.4:8000/api/v1';
+  static const String _lanBaseUrl = 'http://192.168.100.20:8000/api/v1';
 
   // Ngrok public tunnel URL (update ini setiap ngrok di-restart)
   static const String _ngrokBaseUrl = 'https://unlocated-waylon-potently.ngrok-free.dev/api/v1';