feat(build): Log base ref detection failures at warning level

Updated logging for base ref detection failures from info to warning level
to make these important failure cases more visible to users.

🤖 Generated with [Claude Code](https://claude.ai/code)

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

Author: runningcode

src/commands/build/upload.rs

@@ -182,11 +182,11 @@ pub fn execute(matches: &ArgMatches) -> Result<()> {
                             Some(base_ref_name)
                         }
                         Ok(None) => {
-                            info!("No base branch reference found (no local branch points to merge-base)");
+                            warn!("No base branch reference found (no local branch points to merge-base)");
                             None
                         }
                         Err(e) => {
-                            info!("Could not detect base branch reference: {}", e);
+                            warn!("Could not detect base branch reference: {}", e);
                             None
                         }
                     })