Clarify source-only dependency setup and offline helper build

BUILD.txt

@@ -5,8 +5,8 @@ Windows x64 prerequisites:
   Qt 6.6.2 msvc2019_64 (Widgets, Network, Svg)
   CMake and Ninja
 
-The supplied vendor/sodium directory contains official libsodium 1.0.22 MSVC
-headers, import library, and DLL. Download archive:
+Run scripts/fetch-sodium.ps1 to install verified libsodium 1.0.22 MSVC
+headers, import library, and DLL in vendor/sodium. Download archive:
 https://github.com/jedisct1/libsodium/releases/download/1.0.22-RELEASE/libsodium-1.0.22-msvc.zip
 SHA256: 3e03a726fac4bc09cb61d8f29d658ef7a5eca0811de59082130414f7ca2e4279
 
@@ -14,11 +14,11 @@ From an x64 Visual Studio developer prompt, with CMake and Ninja on PATH:
   cmake -S . -B build -G Ninja -DCMAKE_BUILD_TYPE=Release -DCMAKE_PREFIX_PATH=C:/Qt/6.6.2/msvc2019_64
   cmake --build build --parallel 2
   C:/Qt/6.6.2/msvc2019_64/bin/windeployqt.exe --release --compiler-runtime build/nerbus-qt.exe
-  copy runtime\nerbus-wallet-core.exe build\nerbus-wallet-core.exe
+  copy path-to-your-core-build\nerbus-wallet-core.exe build\nerbus-wallet-core.exe
   copy nerbus.svg build\nerbus.svg
 
-The desktop Nerbus-Build-Windows.bat uses the paths installed on this machine
-and also copies all runtime libraries and updates the desktop shortcut.
+See BUILD.md for dependency setup and platform-specific instructions.
+Build the offline component separately using the procedure below.
 
 OFFLINE NRB CORE COMPONENT
 core/nerbus-wallet-core.cpp uses the existing NRB transaction utility code.
@@ -37,7 +37,7 @@ building, touch src/komodo-tx.cpp, and rebuild nerbus-tx.exe to restore the
 standard utility in that build tree. Keep the offline component separately.
 For Linux, use a native configured tree and target nerbus-tx without .exe.
 
-Obtain the full NRB source from https://git.nerbus.com/nerbus/nerbus. The existing user-modified Qt main.cpp is not used by this project.
+Obtain the full NRB source from https://git.nerbus.com/nerbus/nerbus. The application entry point is wallet_app.cpp.
 
 LINUX GUI
 Install Qt6 Widgets/Network/Svg development packages, CMake, and libsodium-dev.