Add bootc-compatible labels implementation and debugging improvements

- Implement complete bootc label support for apt-ostree compose container-encapsulate
- Add containers.bootc, ostree.bootable, ostree.commit, ostree.linux, aptostree.inputhash labels
- Add smart kernel version detection from OSTree tree structure
- Fix container-encapsulate command routing and argument parsing
- Add debug output to main.rs for troubleshooting command routing
- Update CHANGELOG.md with bootc label documentation

This enables full compatibility with bootc-image-builder and the broader bootc ecosystem.
Verified against bootc-image-builder source code analysis.

src/main.rs

@@ -716,6 +716,7 @@ async fn main() -> Result<(), apt_ostree::lib::error::AptOstreeError> {
                     if let Some(ref pbm) = previous_build_manifest {
                         args_vec.extend_from_slice(&["--previous-build-manifest".to_string(), pbm.clone()]);
                     }
+                    println!("🔍 DEBUG: Calling ComposeCommand::execute with args: {:?}", args_vec);
                     commands::advanced::ComposeCommand::new().execute(&args_vec)
                 },
             }