Fix conditional C++ extraction in web console tests

Preserve mutually exclusive preprocessor branches when extracting production C++ for the browser and HWCDC fixtures. Ignore braces in comments, literals and macro definitions, reject mismatched branch joins, and cover the actual repeater command pump with regression tests. Firmware behavior is unchanged.

Validated 93 extractor, official web console, setup GUI and HWCDC checks plus downstream workflow and real PlatformIO metadata checks.

.github/workflows/run-unit-tests.yml

@@ -276,6 +276,7 @@ jobs:
 
       - name: Verify official web console framing and power-saving idle sessions
         run: |
+          python3 -B test/test_cpp_source.py -v
           python3 -B test/test_official_web_console.py -v
           python3 -B test/test_hil_linux_web_serial.py -v
           python3 -B test/test_hil_slowfi_guard.py -v