fix(cli): eliminate TUI flash on key navigation for Latin-script content

The full terminal.clear() fix for complex-script glyph artifacts caused a
visible screen flash on every j/k navigation. Now only clear when the old
or new key actually contains complex-script characters (Arabic, Devanagari,
Bengali, Tamil, Thai, and related Indic/SE Asian scripts). Latin-only keys
navigate without any flash; complex-script keys still get the full repaint
needed to eliminate ratatui diff-renderer ghost cells.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: WendellXY

langcodec-cli/src/editor/mod.rs

@@ -101,15 +101,62 @@ pub fn run_browse_command(opts: BrowseOptions) -> Result<(), String> {
             if let HandlerResult::Quit = handle_event(&mut app, event) {
                 break;
             }
-            // Force full repaint when key selection changes to clear complex-script
-            // glyph artifacts that ratatui's diff renderer leaves behind.
+            // Complex-script glyphs (Arabic, Bengali, Hindi, …) can render wider
+            // than unicode-width reports, leaving ghost cells that ratatui's diff
+            // renderer won't overwrite.  A full terminal clear fixes this, but it
+            // causes a visible flash on every navigation.  Only clear when the
+            // old or new key actually contains complex-script text.
             let cur_key_idx = app.key_list_state.selected();
             if cur_key_idx != prev_key_idx {
+                let old_key = prev_key_idx.and_then(|i| app.filtered_keys.get(i).cloned());
+                let new_key = cur_key_idx.and_then(|i| app.filtered_keys.get(i).cloned());
                 prev_key_idx = cur_key_idx;
-                term.terminal.clear().ok();
+
+                let needs_clear = [old_key, new_key].iter().any(|k| {
+                    k.as_ref().map(|key| {
+                        app.languages.iter().any(|lang| {
+                            app.get_translation(key, lang)
+                                .map(|v| has_complex_scripts(&v))
+                                .unwrap_or(false)
+                        })
+                    }).unwrap_or(false)
+                });
+
+                if needs_clear {
+                    term.terminal.clear().ok();
+                }
             }
         }
     }
 
     Ok(())
 }
+
+/// Returns true if the string contains characters from scripts whose glyphs
+/// commonly render wider than unicode-width predicts (Arabic, Devanagari,
+/// Bengali, Tamil, Thai, Gujarati, Gurmukhi, Kannada, Malayalam, Telugu, …).
+/// Used to decide whether a full terminal clear is needed to avoid artifacts.
+fn has_complex_scripts(s: &str) -> bool {
+    s.chars().any(|c| {
+        let cp = c as u32;
+        matches!(cp,
+            0x0600..=0x06FF  // Arabic
+            | 0x0750..=0x077F // Arabic Supplement
+            | 0xFB50..=0xFDFF // Arabic Pres. Forms-A
+            | 0xFE70..=0xFEFF // Arabic Pres. Forms-B
+            | 0x0900..=0x097F // Devanagari (Hindi, Marathi, …)
+            | 0x0980..=0x09FF // Bengali / Assamese
+            | 0x0A00..=0x0A7F // Gurmukhi (Punjabi)
+            | 0x0A80..=0x0AFF // Gujarati
+            | 0x0B00..=0x0B7F // Odia
+            | 0x0B80..=0x0BFF // Tamil
+            | 0x0C00..=0x0C7F // Telugu
+            | 0x0C80..=0x0CFF // Kannada
+            | 0x0D00..=0x0D7F // Malayalam
+            | 0x0E00..=0x0E7F // Thai
+            | 0x0E80..=0x0EFF // Lao
+            | 0x0F00..=0x0FFF // Tibetan
+            | 0x1000..=0x109F // Myanmar
+        )
+    })
+}