ci: Install go-md2man in main workflow

The bootc-ubuntu-setup action doesn't include go-md2man, which is
needed by the Makefile to generate man pages during the build step.
Add explicit installation step for go-md2man after the environment setup.

Assisted-by: Claude Code (Sonnet 4.5)

Author: cgwalters

.github/workflows/main.yml

@@ -28,6 +28,9 @@ jobs:
       - name: Remove pre-installed bcvk
         run: sudo rm -f /usr/bin/bcvk
 
+      - name: Install go-md2man for man page generation
+        run: sudo apt install -y go-md2man
+
       - name: Setup Rust
         uses: dtolnay/rust-toolchain@stable