feat(cmdline): Enter runs closest command match

Typing a partial command (e.g. `bac`) and pressing Enter with no active
command ran into an "Unknown command" error. Now the top autocomplete
match is highlighted and Enter runs it (`BACKGROUND`), matching standard
DWG command-line behavior.

The fallback only fires when no command family matches the typed verb, so
complete aliases that resolve through a dispatch arm but are absent from
the autocomplete registry (`LT`, `ZO`, …) still run as typed. Programmatic
dispatch (ribbon, plugins, headless automation) is unaffected.

Closes #198

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/update/command.rs

@@ -338,7 +338,7 @@ pub(super) fn on_tab_close(&mut self, idx: usize) -> Task<Message> {
                     return self.focus_cmd_input();
                 }
                 if let Some(cmd) = self.command_line.submit() {
-                    return self.dispatch_command(&cmd);
+                    return self.dispatch_command_or_suggest(&cmd);
                 }
                 // Empty Enter / Space with no active command repeats the
                 // last dispatched command — same shortcut `CommandFinalize`