docs: sync .org with implementation for backend-size, read-raw-byte, SIGWINCH

backend-protocol.org / simple.lisp:
- Replace hard-coded 80x24 prose with full 5-step fallback chain
  (MY_TERM env vars → ioctl fd 0 → ioctl stdout → /dev/tty → 80x24)
- Document return-from pattern (or discards secondary values)

modern-backend.org / modern.lisp:
- Replace simple ioctl-only prose with 4-step fallback chain
- Document env-var pre-check and /dev/tty fallback

text-input.org / input.lisp:
- Update read-raw-byte prose: with-pinned-objects/vector-sap
  instead of alien buffer (code was already correct, prose stale)
- Add missing (require :sb-posix) to SIGWINCH handler code block
- Document :sb-posix requirement in prose

org/text-input.org

@@ -434,9 +434,11 @@ The ~timeout~ keyword uses ~sb-unix:unix-simple-poll~ to implement
 non-blocking reads with a configurable deadline. This is critical for
 the 50ms escape sequence ambiguity resolution in ~%read-escape-sequence~.
 
-Memory management: we allocate a 1-byte alien buffer, read into it, then
-~free-alien~ in an ~unwind-protect~ to prevent leaks even if the read
-is interrupted by a signal.
+Memory management: we use ~sb-sys:with-pinned-objects~ to pin a 1-byte
+~make-array~ vector in memory, obtain its SAP via ~sb-sys:vector-sap~,
+and read directly into the backing storage. This avoids alien allocation
+and manual ~free-alien~ while keeping the GC from moving the buffer
+during the ~unix-read~ syscall.
 
 #+BEGIN_SRC lisp :tangle ../src/components/input.lisp
 (defun read-raw-byte (&key timeout)
@@ -744,7 +746,8 @@ connection. The 500ms gives the terminal ample time to deliver all bytes.
 When the terminal emulator window is resized, the kernel sends SIGWINCH
 to the foreground process group. SBCL's signal handling facility
 (~sb-sys:enable-interrupt~) lets us install a handler that sets this
-flag.
+flag. The ~:sb-posix~ module must be ~require~d first so that the
+~sb-posix:sigwinch~ constant is available.
 
 The main event loop should check this flag after each ~%read-event~
 call and, if set, query the new terminal dimensions and redraw. The
@@ -758,6 +761,7 @@ after handling the resize.
 #+BEGIN_SRC lisp :tangle ../src/components/input.lisp
 #+sbcl
 (eval-when (:load-toplevel :execute)
+  (require :sb-posix)
   (sb-sys:enable-interrupt sb-posix:sigwinch
     (lambda (signal info context)
       (declare (ignore signal info context))