fix(command): keyword/radius input for ribbon-started modify commands (#90)

Starting FILLET/CHAMFER from the ribbon left the command-line field
unfocused, so its Enter arrived as CommandFinalize and discarded a
typed option keyword ("R"/"D"), cancelling the command. Several
related dynamic-input issues surfaced from the same flow:

- CommandFinalize now forwards a non-empty command-line buffer through
  CommandSubmit, so a typed keyword is handled the same whether the
  command was started from the ribbon or the command line.
- sync_dyn_fields shows no coordinate box during an object-pick step
  (needs_entity_pick / needs_structure_point_pick) — there is no point
  to enter there, so typed keywords reach the command line cleanly.
- apply_cmd_result rebuilds the dynamic-input fields on NeedPoint, so a
  step change (object pick -> radius entry) shows the matching box
  immediately and typed digits land in it instead of the command line.
- Object-pick steps now draw a prompt-only hint pill at the cursor
  (no input box).
- FILLET/CHAMFER remember the first pick across a mid-selection radius
  or distance entry, resuming the second pick instead of restarting
  selection.

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

src/ui/overlay.rs

@@ -1251,9 +1251,6 @@ impl canvas::Program<Message> for DynInputCanvas {
         _cursor: mouse::Cursor,
     ) -> Vec<canvas::Geometry> {
         let mut frame = canvas::Frame::new(renderer, bounds.size());
-        if self.boxes.is_empty() {
-            return vec![frame.into_geometry()];
-        }
 
         // Offset the row 14 px right and 20 px below the cursor.
         const OFFSET_X: f32 = 14.0;
@@ -1264,6 +1261,44 @@ impl canvas::Program<Message> for DynInputCanvas {
         const CHAR_W: f32 = FONT_SIZE * 0.62; // monospace-ish width estimate
         const BOX_H: f32 = FONT_SIZE + PAD * 2.0;
 
+        // No input box (a pick step) — draw just the prompt pill at the cursor,
+        // so object-selection steps still get their hint without a field.
+        if self.boxes.is_empty() {
+            if !self.prompt.is_empty() {
+                let pw = (self.prompt.len() as f32 * CHAR_W) + PAD * 2.0;
+                let mut px = self.cursor_screen.x + OFFSET_X;
+                let mut py = self.cursor_screen.y + OFFSET_Y;
+                if px + pw > bounds.width {
+                    px = (self.cursor_screen.x - pw - 4.0).max(0.0);
+                }
+                if py + BOX_H > bounds.height {
+                    py = (self.cursor_screen.y - BOX_H - 4.0).max(0.0);
+                }
+                let prect = canvas::Path::rectangle(
+                    Point { x: px, y: py },
+                    Size {
+                        width: pw,
+                        height: BOX_H,
+                    },
+                );
+                frame.fill(&prect, Color { r: 0.10, g: 0.10, b: 0.12, a: 1.0 });
+                frame.stroke(
+                    &prect,
+                    canvas::Stroke::default()
+                        .with_color(Color { r: 0.35, g: 0.55, b: 0.90, a: 0.9 })
+                        .with_width(1.0),
+                );
+                frame.fill_text(canvas::Text {
+                    content: self.prompt.clone(),
+                    position: Point { x: px + PAD, y: py + PAD },
+                    color: Color { r: 0.70, g: 0.85, b: 0.70, a: 1.0 },
+                    size: iced::Pixels(FONT_SIZE),
+                    ..Default::default()
+                });
+            }
+            return vec![frame.into_geometry()];
+        }
+
         // Each box is "<label>:<value>"; width tracks the text length.
         let texts: Vec<String> = self
             .boxes