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/commands/mod.rs

@@ -754,6 +754,7 @@ inventory::submit!(crate::command::CommandRegistration {
         "SKTOLERANCE",
         "CLIPROMPTLINES",
         "COMMANDLINEFADETIME",
+        "COMMANDLINEOPACITY",
         "COLORTHEME",
         "SELECTIONAREA",
         "SELECTIONAREAOPACITY",

src/app/commands/styleprops.rs

@@ -1149,6 +1149,7 @@ impl OpenCADStudio {
                     | "CURSORSIZE"
                     | "PICKBOX"
                     | "HPASSOC"
+                    | "COMMANDLINEOPACITY"
                     | "CURSORTYPE"
                     | "SNAPANG"
                     | "TEXTFILL"
@@ -2537,6 +2538,22 @@ impl OpenCADStudio {
                                     false,
                                 )),
                             },
+                            "COMMANDLINEOPACITY" => match &value {
+                                Some(v) => match v.parse::<u8>() {
+                                    Ok(n) if (20..=100).contains(&n) => {
+                                        self.command_line.set_opacity_percent(n);
+                                        Ok((format!("COMMANDLINEOPACITY = {n}"), true))
+                                    }
+                                    _ => Err("SETVAR: integer from 20 to 100 required.".into()),
+                                },
+                                None => Ok((
+                                    format!(
+                                        "COMMANDLINEOPACITY = {}",
+                                        self.command_line.opacity_percent()
+                                    ),
+                                    false,
+                                )),
+                            },
                             "COMMANDLINEFADETIME" => match &value {
                                 Some(v) => match v.parse::<i32>() {
                                     Ok(n) if (0..=60000).contains(&n) => {
@@ -3147,6 +3164,7 @@ impl OpenCADStudio {
                                         | "CURSORSIZE"
                                         | "PICKBOX"
                                         | "HPASSOC"
+                                        | "COMMANDLINEOPACITY"
                                         | "CURSORTYPE"
                                         | "SNAPANG"
                                         | "CLIPROMPTLINES"