Gabung app Android Flutter 'Saat Invest' ke repo saat-app (folder flutter/)

Satu repo untuk backend Odoo (addon saat_invest) + app Android.
- flutter/ berisi project Flutter (lib/, android/, pubspec, test)
- Login Odoo JSON-RPC, tab Portofolio+Equity, tab Transaksi, catat jual/beli otomatis sync
- Build .gitignore nested dipakai sehingga artefak build/.dart_tool tak ter-track
Sejarah: gabung flat (satu sejarah backend+app).

flutter/README.md

@@ -0,0 +1,17 @@
+# saat_invest_mobile
+
+A new Flutter project.
+
+## Getting Started
+
+This project is a starting point for a Flutter application.
+
+A few resources to get you started if this is your first Flutter project:
+
+- [Learn Flutter](https://docs.flutter.dev/get-started/learn-flutter)
+- [Write your first Flutter app](https://docs.flutter.dev/get-started/codelab)
+- [Flutter learning resources](https://docs.flutter.dev/reference/learning-resources)
+
+For help getting started with Flutter development, view the
+[online documentation](https://docs.flutter.dev/), which offers tutorials,
+samples, guidance on mobile development, and a full API reference.