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 <noreply@anthropic.com>

src/modules/draw/modify/pedit.rs

@@ -16,11 +16,17 @@ use crate::command::{CadCommand, CmdResult};
 
 pub struct PeditCommand {
     target: Option<Handle>,
+    /// Set once the bare `W` keyword (or the Width button) is chosen: the next
+    /// text input is parsed as the new width instead of an option. (#304)
+    awaiting_width: bool,
 }
 
 impl PeditCommand {
     pub fn new() -> Self {
-        Self { target: None }
+        Self {
+            target: None,
+            awaiting_width: false,
+        }
     }
 }
 
@@ -32,8 +38,24 @@ impl CadCommand for PeditCommand {
     fn prompt(&self) -> String {
         if self.target.is_none() {
             "PEDIT  Select polyline:".into()
+        } else if self.awaiting_width {
+            "PEDIT  Specify new width:".into()
         } else {
-            "PEDIT  Enter option [C=Close O=Open W=Width X=Exit]:".into()
+            "PEDIT  Enter option:".into()
+        }
+    }
+
+    fn options(&self) -> Vec<crate::command::CmdOption> {
+        use crate::command::CmdOption;
+        if self.target.is_none() || self.awaiting_width {
+            vec![]
+        } else {
+            vec![
+                CmdOption::new("Close", "C"),
+                CmdOption::new("Open", "O"),
+                CmdOption::new("Width", "W"),
+                CmdOption::new("eXit", "X"),
+            ]
         }
     }
 
@@ -57,6 +79,21 @@ impl CadCommand for PeditCommand {
         let handle = self.target?;
         let up = text.trim().to_uppercase();
 
+        // Width sub-step: the previous input was a bare `W` (typed or via the
+        // Width button), so this input is the width value. (#304)
+        if self.awaiting_width {
+            let w: f64 = up
+                .replace(',', ".")
+                .parse()
+                .ok()
+                .filter(|&v: &f64| v >= 0.0)?;
+            self.awaiting_width = false;
+            return Some(CmdResult::PeditOp {
+                handle,
+                op: PeditOp::SetWidth(w),
+            });
+        }
+
         match up.as_str() {
             "X" | "EXIT" => return Some(CmdResult::Cancel),
             "C" | "CLOSE" => {
@@ -71,10 +108,17 @@ impl CadCommand for PeditCommand {
                     op: PeditOp::SetClosed(false),
                 })
             }
+            "W" | "WIDTH" => {
+                // Bare width keyword (the Width button): prompt for the value
+                // rather than doing nothing.
+                self.awaiting_width = true;
+                return Some(CmdResult::NeedPoint);
+            }
             _ => {}
         }
 
-        if let Some(rest) = up.strip_prefix("W ").or_else(|| up.strip_prefix("W")) {
+        // Inline shorthand `W <value>`.
+        if let Some(rest) = up.strip_prefix("W ") {
             let w: f64 = rest
                 .trim()
                 .replace(',', ".")