fix(ribbon): dismiss stuck style dropdown on viewport click

The annotation style combo renders its panel inline with no backdrop to
catch outside clicks, so it stayed open after clicking into the viewport
or starting another tool. Close any open ribbon dropdown on viewport
press (left/right/middle) and on command dispatch.

Fixes #50

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

src/app/commands.rs

@@ -7,6 +7,9 @@ use std::path::PathBuf;
 impl OpenCADStudio {
     pub(super) fn dispatch_command(&mut self, cmd: &str) -> 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.
+        self.ribbon.close_dropdown();
         // Cancel any running command before starting a new one.
         if self.tabs[i].active_cmd.is_some() {
             self.tabs[i].scene.clear_preview_wire();