fix(commands): strip _/. name prefixes only when the name as written is unknown

#1584 stripped the prefixes before dispatch, which turned the ribbon's own
internal names (_PCCROPPOLY, _XREFEDIT, _PDFULSNAP, ...) into unknown
commands. A name is now tried as written and retried without its prefixes
only when no family handles it; the Start-tab gate judges the bare name.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/app/command_driver/utilities.rs

@@ -1197,4 +1197,3 @@ impl OpenCADStudio {
         self.run_command_line(trimmed)
     }
 }
-