feat(command): clickable option buttons in the command line (#304)

Commands now expose their step options as clickable buttons rendered
inline beside the command-line prompt, so options need not be typed.

Adds a CmdOption/options() API to CadCommand: each command returns the
options for its current step; the command line renders them as
uppercase buttons and a click feeds the keyword to the command exactly
as if typed (an empty keyword submits like Enter).

Construction commands become "central" — CIRCLE offers [3P/2P/TTR/TTT/
DIAMETER], ELLIPSE [ARC/AXIS], ARC [SCE/SCA/SEA/SER/CSA/3P], RECTANGLE
[ROTATION/CENTER], POLYGON [CIRCUMSCRIBED/EDGE] — each keyword hands off
to the existing dedicated variant command via CmdResult::Dispatch,
instead of the variants only being reachable as isolated commands.

Migrates the existing bracketed-option prompts (PLINE, PEDIT, SPLINE,
SCALE, FILLET, CHAMFER, HATCH, GRADIENT, SOLID, POINT, RAY, XLINE, TRIM,
EXTEND) to the same button API and strips the option text from the
prompt strings, keeping value/coordinate hints. PEDIT's Width option
now enters a value sub-step so the button acts on click.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

src/ui/command_line.rs

@@ -3,6 +3,7 @@
 use iced::time::Instant;
 
 use crate::app::Message;
+use crate::command::CmdOption;
 use iced::widget::{
     button, column, container, opaque, row, text, text_editor, text_input, Space,
 };
@@ -52,6 +53,10 @@ pub struct CommandLine {
     /// The active command step's prompt, mirrored here so a step change
     /// can be detected and the pinned (non-fading) history line updated.
     step_prompt: Option<String>,
+    /// The active command step's clickable options, mirrored here so they
+    /// render as buttons above the input row. Empty when no command is
+    /// active or the current step offers no options. (#304)
+    step_options: Vec<CmdOption>,
 }
 
 #[derive(Clone, Debug)]
@@ -213,6 +218,12 @@ impl CommandLine {
         self.step_prompt = prompt;
     }
 
+    /// Mirror the active command step's clickable options so `view` can render
+    /// them as buttons. Called each frame alongside [`Self::set_step_prompt`].
+    pub fn set_step_options(&mut self, opts: Vec<CmdOption>) {
+        self.step_options = opts;
+    }
+
     /// `true` while at least one history entry is still within the
     /// visible window — the host app uses this to drive a low-frequency
     /// tick subscription so the overlay re-renders and fades the entry
@@ -318,7 +329,48 @@ impl CommandLine {
                     EntryKind::Error => ERR_COLOR,
                     EntryKind::Info => INFO_COLOR,
                 };
-                col.push(container(text(&entry.text).size(11).color(color)).padding([1, 8]))
+                // The current step's prompt is the single pinned line. When the
+                // step offers options, render them as clickable buttons inline
+                // beside the prompt text — so options need never be typed and
+                // don't clutter the prompt string itself. (#304)
+                if entry.pinned && !self.step_options.is_empty() {
+                    let mut r = row![text(&entry.text).size(11).color(color)]
+                        .spacing(6)
+                        .align_y(iced::Center);
+                    for opt in &self.step_options {
+                        let btn = button(
+                            text(opt.label.to_uppercase()).size(11).color(CMD_COLOR),
+                        )
+                        .on_press(Message::CommandOptionPick(opt.keyword.clone()))
+                        .padding([1, 6])
+                        .style(|_: &Theme, status| {
+                            let bg = if matches!(status, button::Status::Hovered) {
+                                Color {
+                                    r: 0.28,
+                                    g: 0.40,
+                                    b: 0.56,
+                                    a: 1.0,
+                                }
+                            } else {
+                                INPUT_ROW_BG
+                            };
+                            button::Style {
+                                background: Some(Background::Color(bg)),
+                                text_color: Color::WHITE,
+                                border: Border {
+                                    color: BORDER_COLOR,
+                                    width: 1.0,
+                                    radius: 3.0.into(),
+                                },
+                                ..Default::default()
+                            }
+                        });
+                        r = r.push(btn);
+                    }
+                    col.push(container(r).padding([1, 8]))
+                } else {
+                    col.push(container(text(&entry.text).size(11).color(color)).padding([1, 8]))
+                }
             });
         let prompt = container(text("Command:").size(11).color(PROMPT_COLOR)).padding([5, 8]);
         // While dynamic input is capturing keystrokes, the command-line