docs(#254): correct Windows exe name to offband_meshcore.exe

The Offband rebrand renamed the Windows executable meshcore_open.exe ->
offband_meshcore.exe (verified: the #244 build produced offband_meshcore.exe).
Only the Windows distribution doc was stale; the Android package/namespace,
MethodChannel names, and macOS/iOS bundle names are deliberately still
meshcore_open (those renames are deferred per the rebrand plan).

docs/windows-distribution-and-versioning.md

@@ -6,7 +6,7 @@ questions raised before the first `feat/64` Windows compile.
 ## 1. Installer / short-term distribution
 
 A Flutter Windows release is a **folder**, not a single exe:
-`build/windows/x64/runner/Release/` = `meshcore_open.exe` + `flutter_windows.dll`
+`build/windows/x64/runner/Release/` = `offband_meshcore.exe` + `flutter_windows.dll`
 + plugin DLLs + `data/` (`app.so`, `flutter_assets/`, `icudtl.dat`). The exe will
 **not** run on its own — it needs the whole folder.