inline terminal emulator, drop xterm.dart dependency

Replace the xterm pub.dev package with owned code under
lib/src/terminal/. Based on xterm.dart v4.0.0 by xuty (MIT).
Quiver LRU replaced with hand-rolled LinkedHashMap cache.
Scrollable removed from TerminalView — scroll events are forwarded
via Listener.onPointerSignal instead. zmodem, debugger, and
suggestion modules stripped as unused.

Also: bundle clide.tmux.conf (no status bar, 50k scrollback,
mouse on, zero escape delay, isolated -L clide socket), bump PTY
read buffer to 64KB, add 2px terminal padding, drop bold
JetBrains Mono registration.

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

lib/builtin/terminal/src/terminal_pane.dart

@@ -7,7 +7,7 @@ import 'package:clide/clide.dart';
 import 'package:clide/kernel/kernel.dart';
 import 'package:clide/widgets/widgets.dart';
 import 'package:flutter/widgets.dart';
-import 'package:xterm/xterm.dart';
+import 'package:clide/src/terminal/terminal.dart';
 
 /// General-purpose terminal pane. Spawns the user's `$SHELL` under the
 /// daemon's PTY (via `pane.spawn`), feeds the `pane.output` event