Add cw_mweb generated_bindings.g.dart stub for desktop builds

Cake's mwebd Go daemon is only built for iOS and Android — no Linux/macOS/
Windows toolchain in their build scripts. ffigen consequently never runs
on those platforms, leaving cw_mweb/lib/mweb_ffi.dart dangling on a
non-existent generated_bindings.g.dart import.

This stub provides type-compatible signatures so the Dart build compiles
on every platform. At runtime, DynamicLibrary.open will fail on desktop
(no libmweb.so/.dll/.dylib shipped) and MWeb features will no-op — standard
non-MWEB Litecoin sends/receives still work fine through cw_bitcoin.

For Android the real bindings are still produced via ffigen against the
libmweb.h Go-generated header, overwriting this stub at build time.

Force-added past the *.g.dart gitignore — this one's a hand-maintained
desktop fallback, not a build artifact.

cw_mweb/lib/generated_bindings.g.dart

@@ -0,0 +1,44 @@
+// Hash Wallet: stub for the FFI bindings normally generated by ffigen from
+// cw_mweb/android/src/main/jniLibs/arm64-v8a/libmweb.h.
+//
+// Upstream Cake only ships MWeb on iOS + Android — no Linux/macOS/Windows
+// build of the Go-based mwebd daemon exists. Without this stub the Dart
+// build fails on those platforms because cw_mweb/lib/mweb_ffi.dart imports
+// MWebFlutter from this file at compile time.
+//
+// At runtime, attempting to use MWeb features will throw because
+// DynamicLibrary.open(libPath) won't find a libmweb.so on desktop. That's
+// fine — Litecoin's MWEB extension is a niche feature most users won't hit,
+// and standard LTC sends/receives still work without it.
+//
+// To get real bindings (e.g. for an Android build): run ffigen against the
+// libmweb.h header generated by `go build -buildmode=c-shared` in cw_mweb/go.
+// See scripts/android/build_mwebd.sh for the canonical Android build.
+
+import 'dart:ffi';
+
+import 'package:ffi/ffi.dart';
+
+class MWebFlutter {
+  MWebFlutter(DynamicLibrary _);
+
+  int StartServer(
+    Pointer<Char> chain,
+    Pointer<Char> dataDir,
+    Pointer<Char> nodeUri,
+    Pointer<Pointer<Char>> errMsg,
+  ) =>
+      0;
+
+  void StopServer() {}
+
+  Pointer<Char> Addresses(
+    Pointer<Uint8> scanSecret,
+    int scanSecretLen,
+    Pointer<Uint8> spendPub,
+    int spendPubLen,
+    int fromIndex,
+    int toIndex,
+  ) =>
+      ''.toNativeUtf8().cast<Char>();
+}