make baseline build & launch cleanly

- onroad.cc: fix screenDisplayMode reference to nvg->screenDisplayMode
  (baseline had a stale reference to the variable after it moved into
  AnnotatedCameraWidget). Restores the original conditional intent.
- ui/SConscript + home.cc: drop QtWebEngine include/link entirely
  (no longer used by any active code).
- build.py: BUILD_ONLY env var spawns the failure TextWindow fully
  detached (own session, /dev/null stdio) so build_only.sh exits and
  caller can capture stderr; spinner binary update uses temp+os.replace
  so a running spinner doesn't ETXTBSY the build.
- build_only.sh: tee build output to /tmp/build.log and propagate
  build.py's exit code via PIPESTATUS.

Verified: build_only.sh completes cleanly, launch_openpilot.sh boots
the manager and spawns the standard process set.

selfdrive/ui/SConscript

@@ -78,19 +78,11 @@ qt_env.Program("_spinner", ["qt/spinner.cc"], LIBS=qt_libs)
 
 
 # Clearpilot
-# Add qtwebengine to build paths
-qt_env['CXXFLAGS'] += ["-I/usr/include/aarch64-linux-gnu/qt5/QtWebEngine"]
-qt_env['CXXFLAGS'] += ["-I/usr/include/aarch64-linux-gnu/qt5/QtWebEngineCore"]
-qt_env['CXXFLAGS'] += ["-I/usr/include/aarch64-linux-gnu/qt5/QtWebEngineWidgets"]
-qt_env['CXXFLAGS'] += ["-I/usr/include/aarch64-linux-gnu/qt5/QtWebChannel"]
-qt_webengine_libs = qt_libs + ['Qt5WebEngineWidgets']
-
 # Create clearpilot tools
 qt_env.Program("/data/openpilot/system/clearpilot/tools/qt_shell", ["/data/openpilot/system/clearpilot/tools/qt_shell.cc"], LIBS=qt_libs)
-# qt_env.Program("/data/openpilot/system/clearpilot/tools/qt_webview", ["/data/openpilot/system/clearpilot/tools/qt_webview.cc"], LIBS=qt_webengine_libs)
 
 # build main UI
-qt_env.Program("ui", qt_src + [asset_obj], LIBS=qt_webengine_libs)
+qt_env.Program("ui", qt_src + [asset_obj], LIBS=qt_libs)
 if GetOption('extras'):
   qt_src.remove("main.cc")  # replaced by test_runner
   qt_env.Program('tests/test_translations', [asset_obj, 'tests/test_runner.cc', 'tests/test_translations.cc'] + qt_src, LIBS=qt_libs)

selfdrive/ui/qt/home.cc

@@ -10,8 +10,6 @@
 #include "selfdrive/ui/qt/widgets/drive_stats.h"
 #include "system/hardware/hw.h"
 
-#include <QWebEngineView>
-
 // HomeWindow: the container for the offroad and onroad UIs
 
 HomeWindow::HomeWindow(QWidget* parent) : QWidget(parent) {

selfdrive/ui/qt/onroad.cc

@@ -78,7 +78,7 @@ void OnroadWindow::updateState(const UIState &s) {
 
   QColor bgColor = bg_colors[s.status];
   
-  if (paramsMemory.getBool("no_lat_lane_change") == 1 || screenDisplayMode == 2) {
+  if (paramsMemory.getBool("no_lat_lane_change") == 1 || nvg->screenDisplayMode == 2) {
     bgColor = bg_colors[STATUS_DISENGAGED];
   }