tlc: phase 17 — skin_dialog adopts shared popup shell

Migrate src/filemanager/skin_dialog.rs::render() from the bespoke
Clear+Block shell (no shadow, square borders) to
terminal::popup::render_popup (rounded borders + MC-matching drop
shadow + centered layout).

This makes skin_dialog visually consistent with all 13 other TLC
dialogs that already use render_popup. The /tmp/5.png screenshot
(showing the skin selector without shadow) is now fixed — every
TLC dialog has identical premium chrome.

Deleted:
  - Duplicate 'centered_rect' helper (replaced by popup::centered_percent_rect)
  - Inline Block construction
  - Manual Clear render

Added:
  - render_drops_shadow_outside_popup test asserts the bottom-right
    cell carries theme.shadow background (assertion of MC's
    tty_draw_box_shadow algorithm at the dialog level).

Tests: 1112 passed (was 1111, +1).

local/recipes/tui/tlc/source/src/filemanager/skin_dialog.rs

@@ -19,11 +19,12 @@
 use ratatui::layout::{Constraint, Direction, Layout, Rect};
 use ratatui::style::{Modifier, Style};
 use ratatui::text::{Line, Span};
-use ratatui::widgets::{Block, Borders, Clear, List, ListItem, Paragraph};
+use ratatui::widgets::{List, ListItem, Paragraph};
 use ratatui::Frame;
 
 use crate::key::Key;
 use crate::terminal::color::{all_skins, find_skin_index, SkinEntry, Theme};
+use crate::terminal::popup::{centered_percent_rect, render_popup};
 
 /// A skin entry surfaced in the selection dialog. The dialog stores
 /// the list as `Vec<SkinEntry>` (see [`crate::terminal::color::SkinEntry`])
@@ -193,23 +194,18 @@ impl SkinDialog {
     /// `theme` supplies the title, list, and hint colours so the
     /// dialog follows the active skin. The dialog itself does not
     /// use a hardcoded colour anywhere in its render path; every
-    /// style derives from the supplied `theme`.
+    /// style derives from the supplied `theme`. The popup shell
+    /// (rounded borders + MC-matching drop shadow) is rendered by
+    /// [`crate::terminal::popup::render_popup`] so all dialogs share
+    /// the same premium chrome.
     pub fn render(&self, frame: &mut Frame, area: Rect, theme: &Theme) {
-        let popup = centered_rect(area, self.width_pct, self.height_pct);
-        frame.render_widget(Clear, popup);
-
-        let block = Block::default()
-            .borders(Borders::ALL)
-            .border_style(Style::default().fg(theme.border))
-            .title(Span::styled(
-                format!(" {} ", crate::locale::t("dialog_title_skin")),
-                Style::default()
-                    .fg(theme.title_fg)
-                    .bg(theme.title_bg)
-                    .add_modifier(Modifier::BOLD),
-            ));
-        let inner = block.inner(popup);
-        frame.render_widget(block, popup);
+        let popup = centered_percent_rect(area, self.width_pct, self.height_pct);
+        let inner = render_popup(
+            frame,
+            popup,
+            crate::locale::t("dialog_title_skin"),
+            theme,
+        );
 
         let chunks = Layout::default()
             .direction(Direction::Vertical)
@@ -308,15 +304,6 @@ impl SkinDialog {
     }
 }
 
-/// Center a popup of `width_pct` × `height_pct` of `area`.
-fn centered_rect(area: Rect, width_pct: f32, height_pct: f32) -> Rect {
-    let w = (area.width as f32 * width_pct.clamp(0.1, 1.0)) as u16;
-    let h = (area.height as f32 * height_pct.clamp(0.1, 1.0)) as u16;
-    let x = area.x + area.width.saturating_sub(w) / 2;
-    let y = area.y + area.height.saturating_sub(h) / 2;
-    Rect::new(x, y, w, h)
-}
-
 #[cfg(test)]
 mod tests {
     use super::*;
@@ -503,4 +490,35 @@ mod tests {
             })
             .expect("render");
     }
+
+    #[test]
+    fn render_drops_shadow_outside_popup() {
+        // After migrating to render_popup the popup shell includes an
+        // MC-matching drop shadow (right strip 2 cells wide + bottom
+        // strip 1 row tall offset by 2 cols). Verify the cells just
+        // outside the popup's bottom-right carry the theme.shadow
+        // background.
+        let d = SkinDialog::new("julia256");
+        let backend = ratatui::backend::TestBackend::new(80, 24);
+        let mut terminal =
+            ratatui::Terminal::new(backend).expect("create test terminal");
+        terminal
+            .draw(|f| {
+                d.render(f, f.area(), &DEFAULT_THEME);
+            })
+            .expect("render");
+        let buf = terminal.backend().buffer().clone();
+        let popup = centered_percent_rect(buf.area, d.width_pct, d.height_pct);
+        let shadow_y = popup.y + popup.height;
+        let shadow_x = popup.x + popup.width;
+        let cell = buf
+            .cell((shadow_x, shadow_y))
+            .expect("bottom-right shadow cell exists");
+        assert_eq!(
+            cell.bg,
+            DEFAULT_THEME.shadow,
+            "shadow cell at ({shadow_x},{shadow_y}) should carry shadow bg; got {:?}",
+            cell.bg
+        );
+    }
 }