Terminal loop, virtual buffers, yank bound

- kte refuses to start when stdin is not a terminal: piped bytes were
  executed as editor commands (C-k s plus a path writes a file), and
  after EOF the loop spun at full CPU with no way to quit.
- The terminal frontend handles all pending input before drawing (a
  paste used to cost a frame and a full redraw per character) and
  redraws only after input, a resize or deferred opens, else once a
  second. The renderer caches, per row and buffer version, where the
  horizontally scrolled part of a line starts and the cursor's render
  column, instead of rescanning the line every frame. Idle CPU with the
  cursor at the end of a 20 MB line: one full core -> ~1%.
- Buffers with a virtual name (+HELP+) are not journaled and saving one
  asks for a file name; it used to write ./+HELP+ and journal under
  that path.
- Yank with a repeat count is capped at 256 MiB in total instead of
  reserving count x size bytes (C-u 1000000 C-y of a large kill).
- Remove an overload clang reports as unused (-Werror on macOS).

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

Swap.cc

@@ -346,8 +346,8 @@ SwapManager::Rehome(Buffer *old_addr, Buffer *new_addr)
 void
 SwapManager::Attach(Buffer *buf)
 {
-	if (!buf)
-		return;
+	if (!buf || buf->IsVirtual())
+		return; // e.g. +HELP+: nothing to recover, and its name is not a path
 	std::lock_guard<std::mutex> lg(mtx_);
 	const bool fresh = journals_.find(buf) == journals_.end();
 	JournalCtx &ctx  = journals_[buf];