Bug: Apply SELinux context after binary replacement (#1678)

- Move SELinux context handling to internal/ghupdate for reuse
- Make chcon a true fallback (only runs if semanage/restorecon unavailable)
- Handle existing semanage rules with -m (modify) after -a (add) fails
- Apply SELinux handling to both agent and hub updates
- Add tests with proper skip behavior for SELinux systems

---------

Co-authored-by: henrygd <hank@henrygd.me>

internal/hub/update.go

@@ -45,6 +45,11 @@ func Update(cmd *cobra.Command, _ []string) {
 		fmt.Printf("Warning: failed to set executable permissions: %v\n", err)
 	}
 
+	// Fix SELinux context if necessary
+	if err := ghupdate.HandleSELinuxContext(exePath); err != nil {
+		ghupdate.ColorPrintf(ghupdate.ColorYellow, "Warning: SELinux context handling: %v", err)
+	}
+
 	// Try to restart the service if it's running
 	restartService()
 }