fix(render): replace SMP emoji with stable BMP glyphs to fix layout on Windows terminals

Emoji in U+1F000+ have no stable column-width contract across terminal
emulators.  On cmd.exe/PowerShell they render as 1-column placeholder
boxes even though unicode_width reports 2; on WezTerm/Alacritty with
certain font stacks the rendered width can be off by one column.  Both
cases break layout arithmetic in the header and file-tree widgets.

Changes:
- header.rs: replace 🐳 (U+1F433, 2-wide) with ◆ (U+25C6, always 1-wide)
  in the "max" reasoning-effort chip
- file_tree.rs: drop the 📁/📄 (U+1F4C1/U+1F4C4) entry-icon prefix; the
  ▼/▶ expand marker already distinguishes dirs from files

Fixes #1314

crates/tui/src/tui/file_tree.rs

@@ -333,14 +333,12 @@ pub fn render_file_tree(
             } else {
                 "  "
             };
-            let icon = if entry.is_dir {
-                "\u{1F4C1} "
-            } else {
-                "\u{1F4C4} "
-            }; // 📁 / 📄
+            // No separate icon: the ▼/▶ expand marker already signals dirs,
+            // and SMP emoji (📁/📄, U+1F4C1/U+1F4C4) render at inconsistent
+            // column widths across terminals, breaking layout. See issue #1314.
 
             // Build the display text.
-            let raw = format!("{indent}{expand_marker}{icon}{}", entry.name);
+            let raw = format!("{indent}{expand_marker}{}", entry.name);
             let display = truncate_line_to_width(&raw, content_width.max(1));
 
             let style = if is_selected {

crates/tui/src/tui/widgets/header.rs

@@ -250,7 +250,10 @@ impl<'a> HeaderWidget<'a> {
         let body = if !include_prefix {
             trimmed.to_string()
         } else if trimmed.eq_ignore_ascii_case("max") || trimmed.eq_ignore_ascii_case("maximum") {
-            format!("\u{1F433} {trimmed}")
+            // Use a non-emoji diamond (U+25C6, always 1 column) instead of an
+            // SMP emoji whose rendered width is inconsistent across terminals
+            // (cmd/PowerShell, WezTerm, Alacritty). See issue #1314.
+            format!("\u{25C6} {trimmed}")
         } else {
             format!("\u{00B7} {trimmed}")
         };