feat(terminal): bundle JetBrainsMono Nerd Font for terminal glyphs

The terminal tabs and inline terminal panel used xterm's default
`monospace`, which lacks Nerd Font glyphs — so TUIs like yazi rendered
box-drawing, Powerline symbols and file-type icons as tofu.

Declare a `JetBrainsMono Nerd Font` family in pubspec and apply it via
`TerminalStyle` (with a Cascadia Code / Fira Code / system-monospace
fallback chain) to the `TerminalView` in both `terminal_page.dart`
(tabs) and `inline_terminal_panel.dart` (mobile split view). The font
binary (nerd-fonts v3.3.0) is bundled like RustDesk's other assets;
`flutter/fetch_font.sh` can refresh it. Client-only; the server stays stock.

flutter/fetch_font.sh

@@ -0,0 +1,22 @@
+#!/usr/bin/env bash
+# Downloads JetBrainsMono Nerd Font for terminal glyph support (yazi, etc.)
+set -euo pipefail
+
+FONT_DIR="$(dirname "$0")/assets"
+FONT_FILE="$FONT_DIR/JetBrainsMonoNerdFont-Regular.ttf"
+FONT_URL="https://github.com/ryanoasis/nerd-fonts/releases/download/v3.3.0/JetBrainsMono.zip"
+
+if [ -f "$FONT_FILE" ]; then
+  echo "Font already exists: $FONT_FILE"
+  exit 0
+fi
+
+echo "Downloading JetBrainsMono Nerd Font..."
+mkdir -p "$FONT_DIR"
+TMPZIP=$(mktemp /tmp/JetBrainsMono.XXXXXX.zip)
+trap 'rm -f "$TMPZIP"' EXIT
+
+wget -q "$FONT_URL" -O "$TMPZIP"
+unzip -q -o "$TMPZIP" "JetBrainsMonoNerdFont-Regular.ttf" -d /tmp/
+mv /tmp/JetBrainsMonoNerdFont-Regular.ttf "$FONT_FILE"
+echo "Installed: $FONT_FILE ($(du -h "$FONT_FILE" | cut -f1))"

flutter/lib/desktop/pages/inline_terminal_panel.dart

@@ -98,8 +98,18 @@ class _InlineTerminalPanelState extends State<InlineTerminalPanel> {
 
   // Slightly larger than xterm's default (13) with comfortable line height for
   // legibility on a phone-sized split view.
-  static const TerminalStyle _textStyle =
-      TerminalStyle(fontSize: 14, height: 1.3);
+  static const TerminalStyle _textStyle = TerminalStyle(
+    fontSize: 14,
+    height: 1.3,
+    fontFamily: 'JetBrainsMono Nerd Font',
+    fontFamilyFallback: [
+      'Cascadia Code',
+      'Fira Code',
+      'Menlo',
+      'Consolas',
+      'monospace',
+    ],
+  );
 
   // Show the on-screen special-keys bar (Esc/Ctrl/Alt/arrows/…). Honours the
   // same option as the stock mobile terminal (default on).

flutter/lib/desktop/pages/terminal_page.dart

@@ -47,6 +47,18 @@ class _TerminalPageState extends State<TerminalPage>
   static const EdgeInsets _defaultTerminalPadding =
       EdgeInsets.symmetric(horizontal: 5.0, vertical: 2.0);
 
+  static const TerminalStyle _terminalStyle = TerminalStyle(
+    fontSize: 14,
+    fontFamily: 'JetBrainsMono Nerd Font',
+    fontFamilyFallback: [
+      'Cascadia Code',
+      'Fira Code',
+      'Menlo',
+      'Consolas',
+      'monospace',
+    ],
+  );
+
   late FFI _ffi;
   late TerminalModel _terminalModel;
   double? _cellHeight;
@@ -199,6 +211,7 @@ class _TerminalPageState extends State<TerminalPage>
             _terminalModel.terminal,
             controller: _terminalModel.terminalController,
             focusNode: _terminalFocusNode,
+            textStyle: _terminalStyle,
             // Note: autofocus is not used here because focus is managed manually
             // via _onTabStateChanged() to handle tab switching properly.
             backgroundOpacity: 0.7,

flutter/pubspec.yaml

@@ -172,6 +172,9 @@ flutter:
     - family: More
       fonts:
         - asset: assets/more.ttf
+    - family: JetBrainsMono Nerd Font
+      fonts:
+        - asset: assets/JetBrainsMonoNerdFont-Regular.ttf
 
   # An image asset can refer to one or more resolution-specific "variants", see
   # https://flutter.dev/assets-and-images/#resolution-aware.