concore build --auto-build exits 0 and says "Workflow ready!" when the build fails #640

When the generated build script fails, concore build --auto-build prints "Build failed" but then still prints the green "Workflow ready!" panel and exits with code 0, so scripts and CI can't tell that the build failed.

Steps (Windows 11, dev @ 8f3e444):

1. concore init p
2. concore build p/workflow.graphml --source p/src --output out --type docker --auto-build
   (on Windows the generated bash build script can't be run by cmd, so the build fails)
3. Output shows Build failed, then ✓ Workflow ready!; echo %errorlevel% → 0.

Cause: in concore_cli/commands/build.py the auto-build except subprocess.CalledProcessError block prints the error and falls through to the success panel. The generation step a few lines above re-raises in the same situation, which cli.py turns into Error: ... and exit 1.

I have a small fix with a test and will open a PR against dev.