fix fresh-install build: add preflight script, restore third_party binaries, remove WebEngine dep

- Add build_preflight.sh to create obj/ dirs that git can't track (body/board/obj, panda/board/obj)
- Wire preflight into build_only.sh and launch_chffrplus.sh
- Restore missing third_party binaries (libyuv, snpe, acados, maplibre) that were text pointers
- Remove dead Qt5WebEngineWidgets dependency from UI SConscript

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

selfdrive/ui/SConscript

@@ -77,20 +77,11 @@ qt_env.Program("_text", ["qt/text.cc"], LIBS=qt_libs)
 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
+# 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)