refactor: group ui/ style+popup dirs, rename cmd_result driver

- Group the flat src/ui/ dir: move the 9 style editors into ui/style/
  (dimstyle, mleaderstyle, mlstyle, plotstyle, textstyle, tablestyle,
  point_style, style_list, style_manager) and the 6 popups into
  ui/popup/ (cycle, isolate, scale, selection_filter, snap, units).
  Call sites repointed to crate::ui::style::/crate::ui::popup::; no
  compat re-exports. ui/ root drops from 36 to 21 files.
- Rename app/cmd_result.rs -> app/command_driver.rs: the file is the
  StepInput->feed_command driver, not the CmdResult type (which lives
  in command.rs). Name now matches contents.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/ui/style/style_list.rs

@@ -0,0 +1,80 @@
+//! Shared style-manager list row.
+//!
+//! Every style manager renders the same left-hand list of style names where a
+//! single click selects and a double click renames inline.
+//!
+//! The whole row is a `mouse_area` (not a `button`): an inner interactive
+//! widget would capture the press and the parent `mouse_area` would never see
+//! the second click, so `on_double_click` would never fire. `mouse_area`
+//! carries both `on_press` (select) and `on_double_click` (rename) itself.
+
+use crate::app::{Message, StyleKind};
+use iced::widget::{container, mouse_area, row, text, text_input};
+use iced::{Background, Color, Element, Fill, Theme};
+
+/// Shared id for the inline rename field, so the rename-start handler can focus
+/// it the moment the row turns editable.
+pub fn rename_input_id() -> iced::widget::Id {
+    iced::widget::Id::new("style-rename-input")
+}
+
+const TEXT: Color = Color {
+    r: 0.88,
+    g: 0.88,
+    b: 0.88,
+    a: 1.0,
+};
+const ACTIVE: Color = Color {
+    r: 0.20,
+    g: 0.40,
+    b: 0.70,
+    a: 1.0,
+};
+const CURRENT_CHECK: Color = Color {
+    r: 0.30,
+    g: 0.82,
+    b: 0.36,
+    a: 1.0,
+};
+
+/// One row of the style list. Renders an editable `text_input` when `name` is
+/// the style being renamed (`rename_active`), otherwise a selectable row whose
+/// double click starts the rename. The current style gets a green ✓.
+pub fn item<'a>(
+    name: &str,
+    is_current: bool,
+    is_selected: bool,
+    kind: StyleKind,
+    on_select: Message,
+    rename_active: Option<&str>,
+    rename_buf: &'a str,
+) -> Element<'a, Message> {
+    if rename_active == Some(name) {
+        text_input("", rename_buf)
+            .id(iced::widget::Id::new("style-rename-input"))
+            .on_input(Message::StyleRenameEdit)
+            .on_submit(Message::StyleRenameCommit(kind))
+            .size(11)
+            .padding([4, 8])
+            .width(Fill)
+            .into()
+    } else {
+        // Fixed-width ✓ column keeps every name left-aligned whether or not the
+        // row is current.
+        let check = crate::ui::icons::check_cell(is_current, CURRENT_CHECK);
+        let label = row![check, text(name.to_string()).size(11).color(TEXT)]
+            .align_y(iced::Center);
+        let cell = container(label)
+            .padding([4, 8])
+            .width(Fill)
+            .style(move |_: &Theme| container::Style {
+                background: is_selected.then_some(Background::Color(ACTIVE)),
+                text_color: Some(TEXT),
+                ..Default::default()
+            });
+        mouse_area(cell)
+            .on_press(on_select)
+            .on_double_click(Message::StyleRenameStart(kind, name.to_string()))
+            .into()
+    }
+}