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.h

@@ -34,6 +34,7 @@
  *    - Direct PieceTable access for new editing operations
  */
 #pragma once
+#include <atomic>
 
 #include <algorithm>
 #include <cstddef>
@@ -352,6 +353,15 @@ public:
 	}
 
 
+	// Identity of this document, stable for its lifetime, including when the
+	// Buffer object is moved (e.g. by the editor's buffer vector). Copies get
+	// a new id. Use it, not the object's address, to key per-buffer caches.
+	[[nodiscard]] std::uint64_t Id() const
+	{
+		return id_;
+	}
+
+
 	[[nodiscard]] bool Dirty() const
 	{
 		return dirty_;
@@ -703,6 +713,13 @@ private:
 	std::string filename_;
 	bool is_file_backed_              = false;
 	bool is_virtual_                  = false;
+	std::uint64_t id_                 = NextBufferId();
+
+	static std::uint64_t NextBufferId()
+	{
+		static std::atomic<std::uint64_t> next{1};
+		return next.fetch_add(1);
+	}
 	bool dirty_                       = false;
 	bool read_only_                   = false;
 	bool mark_set_                    = false;