feat(ui): shared dropdown popup width calculation with wide-character support

- Add dropdown_popup_width helper in common.rs replacing magic formula heuristics
- Implement is_wide range table to count East Asian Wide/Fullwidth (CJK) glyphs double for localized strings
- Calibrate unit scale factor to 0.68 * font_size preserving existing width behavior at font size 11
- Apply shared calculation across viewport controls and ribbon dropdowns
- Update unit tests to verify width calculation on standard and CJK labels

src/app/view/controls.rs

@@ -131,12 +131,13 @@ pub(super) fn viewport_controls<'a>(
     );
 
     let preview_mode = render_mode_preview.unwrap_or(render_mode);
-    let max_label_len = render_modes
-        .iter()
-        .map(|c| c.to_string().chars().count())
-        .max()
-        .unwrap_or(0);
-    let dropdown_w = (max_label_len as f32 * 7.5 + 46.0).max(180.0);
+    let mode_names: Vec<String> = render_modes.iter().map(|c| c.to_string()).collect();
+    let dropdown_w = crate::ui::style::common::dropdown_popup_width(
+        mode_names.iter().map(|s| s.as_str()),
+        11.0,
+        46.0,
+        180.0,
+    );
 
     let mut choices = column![].spacing(2).width(Length::Fill);
     for choice in render_modes {
@@ -445,13 +446,30 @@ mod tests {
             .map(|c| c.label.chars().count())
             .max()
             .unwrap_or(0);
-        let dropdown_w = (max_label_len as f32 * 7.5 + 46.0).max(180.0);
+        let dropdown_w = crate::ui::style::common::dropdown_popup_width(
+            crate::modules::view::visual_style::VISUAL_STYLES
+                .iter()
+                .map(|c| c.label),
+            11.0,
+            46.0,
+            180.0,
+        );
 
         // Longest default label is "Gouraud Shaded + Edges" (22 chars)
         assert_eq!(max_label_len, 22);
         // Computed width should easily fit the 22-char label + checkmark + padding
         assert!(dropdown_w >= 210.0);
 
+        // CJK labels count wide characters double
+        let cjk_labels = ["二维线框", "着色+边"];
+        let cjk_w = crate::ui::style::common::dropdown_popup_width(
+            cjk_labels.iter().copied(),
+            11.0,
+            46.0,
+            180.0,
+        );
+        assert_eq!(cjk_w, 180.0);
+
         for style in crate::modules::view::visual_style::VISUAL_STYLES {
             assert!(!style.label.contains('\n'), "Label should be a single line");
         }

src/ui/ribbon/mod.rs

@@ -853,6 +853,7 @@ impl Ribbon {
                 let label_el =
                     text(t!(*label))
                         .size(11)
+                        .wrapping(iced::advanced::text::Wrapping::None)
                         .style(move |theme: &Theme| iced::widget::text::Style {
                             color: (!is_current).then_some(
                                 theme
@@ -880,11 +881,22 @@ impl Ribbon {
             })
             .collect();
 
+        let labels: Vec<String> = items
+            .iter()
+            .map(|(_, label, _)| t!(*label).to_string())
+            .collect();
+        let panel_w = crate::ui::style::common::dropdown_popup_width(
+            labels.iter().map(|s| s.as_str()),
+            11.0,
+            68.0,
+            190.0,
+        );
+
         let panel = container(column(rows))
             .style(popup_panel_style)
-            .width(Length::Fixed(190.0));
+            .width(Length::Fixed(panel_w));
 
-        let (align_right, h_pad, top) = self.dd_anchor(open_id, 190.0, win.0);
+        let (align_right, h_pad, top) = self.dd_anchor(open_id, panel_w, win.0);
         Some(dropdown_backdrop(position_ribbon_dropdown(
             panel.into(),
             align_right,

src/ui/style/common.rs

@@ -73,3 +73,33 @@ pub(crate) fn accessible_accent(accent: Color, bg: Color, fallback: Color) -> Co
 pub(crate) fn canvas_is_light(bg: [f32; 4]) -> bool {
     wcag_luminance(Color::from_rgb(bg[0], bg[1], bg[2])) > 0.5
 }
+
+/// True if a character is East Asian Wide or Fullwidth (CJK ideographs, kana, hangul, fullwidth forms).
+pub(crate) fn is_wide(c: char) -> bool {
+    let u = c as u32;
+    matches!(
+        u,
+        0x1100..=0x115F   // Hangul Jamo
+        | 0x2E80..=0xA4CF // CJK Radicals, Kangxi, Hiragana, Katakana, Bopomofo, Hangul Compatibility, CJK Unified Ideographs, Yi
+        | 0xAC00..=0xD7A3 // Hangul Syllables
+        | 0xF900..=0xFAFF // CJK Compatibility Ideographs
+        | 0xFE30..=0xFE4F // CJK Compatibility Forms
+        | 0xFF01..=0xFF60 // Fullwidth ASCII variants
+        | 0xFFE0..=0xFFE6 // Fullwidth symbol variants
+        | 0x20000..=0x2FA1F // CJK Unified Ideographs Extension B-F, Compatibility Supplement
+    )
+}
+
+/// Estimated popup width for a vertical list of labels. Wide (CJK) glyphs
+/// count double so localized labels via t!() don't truncate.
+pub fn dropdown_popup_width<'a>(
+    labels: impl Iterator<Item = &'a str>,
+    font_size: f32,
+    chrome: f32,
+    min: f32,
+) -> f32 {
+    let max_units = labels
+        .map(|l| l.chars().map(|c| if is_wide(c) { 2.0 } else { 1.0 }).sum::<f32>())
+        .fold(0.0f32, f32::max);
+    (max_units * font_size * 0.68 + chrome).max(min)
+}