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/commands/mod.rs

@@ -36,6 +36,22 @@ impl OpenCADStudio {
     }
 
     pub(super) fn dispatch_command(&mut self, cmd: &str) -> Task<Message> {
+        self.dispatch_command_inner(cmd, false)
+    }
+
+    /// Dispatch a verb typed at the interactive command line, falling back to
+    /// the closest autocomplete suggestion when the verb matches no command
+    /// family. Lets a partial command run on Enter (`BAC` → `BACKGROUND`),
+    /// the standard DWG command-line behavior. The fallback only fires for
+    /// genuinely unknown verbs, so complete aliases that resolve through a
+    /// dispatch family (`LT`, `ZO`, …) still run as typed. Programmatic
+    /// callers (ribbon, plugins, headless automation) use `dispatch_command`
+    /// and never get silent substitution.
+    pub(super) fn dispatch_command_or_suggest(&mut self, cmd: &str) -> Task<Message> {
+        self.dispatch_command_inner(cmd, true)
+    }
+
+    fn dispatch_command_inner(&mut self, cmd: &str, allow_suggest: bool) -> Task<Message> {
         let i = self.active_tab;
         // Starting a command closes any open ribbon dropdown (e.g. a style
         // combo left open) so it does not stay stuck behind the new tool.
@@ -126,7 +142,17 @@ impl OpenCADStudio {
             return t;
         }
 
-        // No family matched.
+        // No family matched. From the interactive command line, run the
+        // closest autocomplete suggestion instead of erroring, so a partial
+        // command completes on Enter (`BAC` → `BACKGROUND`). The verb's own
+        // input was already cleared, so rank against `cmd` directly.
+        if allow_suggest {
+            if let Some(top) = crate::ui::command_line::ranked_matches(cmd).first().copied() {
+                if !top.eq_ignore_ascii_case(cmd) {
+                    return self.dispatch_command_inner(top, false);
+                }
+            }
+        }
         self.command_line
             .push_error(&format!("Unknown command: {cmd}"));
         self.finish_dispatch(cmd)

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`