Fix CI: use 64-bit inetc plugin for MSYS2 NSIS

MSYS2 mingw64 NSIS is a 64-bit build that needs amd64-unicode plugins.
Copy the amd64-unicode INetC.dll to Plugins/unicode/ instead of x86.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.github/workflows/build-all.yml

@@ -171,25 +171,10 @@ jobs:
           cd /tmp
           curl -L -o Inetc.zip "https://nsis.sourceforge.io/mediawiki/images/c/c9/Inetc.zip"
           unzip -o Inetc.zip -d inetc_extract
-          echo "=== Existing NSIS plugin dirs ==="
-          ls -la "$NSIS_DIR/Plugins/" || true
-          echo "=== Zip contents ==="
-          find inetc_extract/Plugins -name "*.dll" 2>/dev/null || true
-          # Copy all variants - NSIS will use whichever matches its architecture
-          for arch in x86-unicode x86-ansi amd64-unicode; do
-            if [ -d "inetc_extract/Plugins/$arch" ]; then
-              mkdir -p "$NSIS_DIR/Plugins/$arch"
-              cp inetc_extract/Plugins/$arch/INetC.dll "$NSIS_DIR/Plugins/$arch/"
-              echo "Installed INetC.dll to $NSIS_DIR/Plugins/$arch/"
-            fi
-          done
-          # Also copy x86-unicode to generic 'unicode' dir as fallback
-          if [ -f "inetc_extract/Plugins/x86-unicode/INetC.dll" ]; then
-            mkdir -p "$NSIS_DIR/Plugins/unicode"
-            cp inetc_extract/Plugins/x86-unicode/INetC.dll "$NSIS_DIR/Plugins/unicode/"
-          fi
-          echo "=== Final plugin dirs ==="
-          find "$NSIS_DIR/Plugins" -name "INetC.dll" 2>/dev/null || echo "WARNING: no INetC.dll found"
+          # MSYS2 mingw64 NSIS is 64-bit, needs amd64-unicode plugin in Plugins/unicode/
+          mkdir -p "$NSIS_DIR/Plugins/unicode"
+          cp inetc_extract/Plugins/amd64-unicode/INetC.dll "$NSIS_DIR/Plugins/unicode/"
+          echo "Installed 64-bit INetC.dll to $NSIS_DIR/Plugins/unicode/"
 
       - name: Build NSIS installer
         run: makensis //DVERSION=$VERSION contrib/nsis/setup.nsi