feat(command-line): adjustable command line opacity

COMMANDLINEOPACITY (20-100 percent, default 100) and a slider under
Options > Display make the floating command line's panels see-through,
so the drawing stays visible behind it. The input field stays opaque
for legibility. The value is an application setting that persists.

Refs #1494

Co-Authored-By: Claude Opus 5.5 <[email protected]>

src/app/update/file.rs

@@ -847,6 +847,7 @@ impl OpenCADStudio {
             quick_properties: self.quick_properties,
             language: self.language,
             cliprompt_lines: crate::app::settings::clamp_clipromptlines(self.cliprompt_lines),
+            command_line_opacity: self.command_line.opacity_percent(),
             commandline_fade_ms: crate::app::settings::clamp_commandline_fade_ms(
                 self.commandline_fade_ms,
             ),
@@ -999,6 +1000,7 @@ impl OpenCADStudio {
         self.cliprompt_lines = crate::app::settings::clamp_clipromptlines(s.cliprompt_lines);
         self.command_line
             .set_cliprompt_lines(self.cliprompt_lines.clamp(0, 50) as u8);
+        self.command_line.set_opacity_percent(s.command_line_opacity);
         self.commandline_fade_ms =
             crate::app::settings::clamp_commandline_fade_ms(s.commandline_fade_ms);
         self.command_line

src/app/update/mod.rs

@@ -9057,6 +9057,12 @@ impl OpenCADStudio {
                 Task::none()
             }
 
+            Message::CommandLineOpacityChanged(percent) => {
+                self.command_line.set_opacity_percent(percent);
+                self.persist_settings_if_changed();
+                Task::none()
+            }
+
             Message::CommandLineFadeChanged(ms) => {
                 let ms = crate::app::settings::clamp_commandline_fade_ms(ms);
                 self.commandline_fade_ms = ms;