Force a UTF-8 ctype, stable buffer ids, redraw after deferred opens

- main: when the environment's locale is not UTF-8 (LANG unset, C/POSIX),
  switch LC_CTYPE to a UTF-8 locale so ncurses delivers and draws
  multibyte characters instead of dropping them.
- Buffer::Id(): a process-unique id that survives moves and is fresh for
  copies. The terminal renderer's skip and cursor caches and the reload
  confirmation now key on it rather than the buffer's address, which is
  reused after a buffer is closed.
- The reload confirmation is cancelled by any other command, like the
  quit confirmation.
- TerminalFrontend redraws when a deferred open starts a prompt or sets a
  status (e.g. the swap recovery question), not only when a buffer opens.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015rcVQiiWyTzoNrsvLSaAfB

Buffer.cc

@@ -390,6 +390,7 @@ Buffer::operator=(const Buffer &other)
 	filename_         = other.filename_;
 	is_file_backed_   = other.is_file_backed_;
 	is_virtual_       = other.is_virtual_;
+	id_               = NextBufferId(); // a copy is a different document
 	dirty_            = other.dirty_;
 	read_only_        = other.read_only_;
 	mark_set_         = other.mark_set_;
@@ -436,6 +437,7 @@ Buffer::Buffer(Buffer &&other) noexcept
 	  filename_(std::move(other.filename_)),
 	  is_file_backed_(other.is_file_backed_),
 	  is_virtual_(other.is_virtual_),
+	  id_(other.id_),
 	  dirty_(other.dirty_),
 	  read_only_(other.read_only_),
 	  mark_set_(other.mark_set_),
@@ -487,6 +489,7 @@ Buffer::operator=(Buffer &&other) noexcept
 	filename_             = std::move(other.filename_);
 	is_file_backed_       = other.is_file_backed_;
 	is_virtual_           = other.is_virtual_;
+	id_                   = other.id_;
 	dirty_                = other.dirty_;
 	read_only_            = other.read_only_;
 	mark_set_             = other.mark_set_;