fix: build radiosonde_auto_rx C decoders (dft_detect, fsk_demod, etc.)

setup.sh and Dockerfile were installing the Python package and copying
files but skipping the build.sh step that compiles the C decoders.
This caused "Binary dft_detect does not exist" at runtime.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

setup.sh

@@ -848,6 +848,12 @@ install_radiosonde_auto_rx() {
       }
     fi
 
+    info "Building radiosonde_auto_rx C decoders..."
+    if ! bash build.sh; then
+      warn "Failed to build radiosonde_auto_rx decoders"
+      exit 1
+    fi
+
     info "Installing to ${install_dir}..."
     refresh_sudo
     $SUDO mkdir -p "$install_dir/auto_rx"