Set local GOMODCACHE alongside GOCACHE for builds

scripts/build-linux.sh

@@ -46,7 +46,8 @@ echo "🔨 Building VideoTools..."
 # Fyne needs cgo for GLFW/OpenGL bindings; build with CGO enabled.
 export CGO_ENABLED=1
 export GOCACHE="$PROJECT_ROOT/.cache/go-build"
-mkdir -p "$GOCACHE"
+export GOMODCACHE="$PROJECT_ROOT/.cache/go-mod"
+mkdir -p "$GOCACHE" "$GOMODCACHE"
 if go build -o "$BUILD_OUTPUT" .; then
     echo "✓ Build successful! (VideoTools $APP_VERSION)"
     echo ""