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

TerminalFrontend.h

@@ -2,6 +2,7 @@
  * TerminalFrontend - couples TerminalInputHandler + TerminalRenderer and owns ncurses lifecycle
  */
 #pragma once
+#include <chrono>
 #include <termios.h>
 #include <signal.h>
 
@@ -32,6 +33,9 @@ private:
 	TerminalRenderer renderer_{};
 	int prev_r_ = 0;
 	int prev_c_ = 0;
+	// Redraw only when something may have changed (see Step).
+	bool first_frame_ = true;
+	std::chrono::steady_clock::time_point last_draw_{};
 	// Saved terminal attributes to restore on shutdown
 	bool have_orig_tio_ = false;
 	struct termios orig_tio_{};