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/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)
+}