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

src/backend/modern.lisp

@@ -162,9 +162,9 @@ as a fallback when a keyword is not in *named-colors*.")
   (values))
 
 (defmethod backend-size ((b modern-backend))
-  ;; MY_TERM_COLS/MY_TERM_ROWS — set by the passepartout script
-  ;; before exec sbcl. Check FIRST with return-from so both
-  ;; values (cols and rows) are preserved (or discards secondaries).
+  ;; MY_TERM_COLS/MY_TERM_ROWS — set by the calling script.
+  ;; Check FIRST with return-from so both values (cols and rows)
+  ;; are preserved (or discards secondaries).
   (let ((cstr (sb-ext:posix-getenv "MY_TERM_COLS"))
         (rstr (sb-ext:posix-getenv "MY_TERM_ROWS")))
     (when (and cstr rstr)
@@ -184,8 +184,8 @@ as a fallback when a keyword is not in *named-colors*.")
                        (values (sb-alien:deref winsize 1)  ;; cols
                                (sb-alien:deref winsize 0)))) ;; rows
                 (sb-alien:free-alien winsize))))
-        (when (and cols rows (> cols 0) (> rows 0))
-          (values cols rows)))
+          (when (and cols rows (> cols 0) (> rows 0))
+            (values cols rows)))
       ;; Direct ioctl on /dev/tty.
       (ignore-errors
         (let ((tty-fd (sb-unix:unix-open "/dev/tty" 0 0)))
@@ -198,7 +198,7 @@ as a fallback when a keyword is not in *named-colors*.")
                        (let ((cols (sb-alien:deref winsize 1))
                              (rows (sb-alien:deref winsize 0)))
                          (values cols rows)))))
-               (sb-unix:unix-close tty-fd)))))
+              (sb-unix:unix-close tty-fd)))))
       (values 80 24)))
 
 (defmethod backend-write ((b modern-backend) string)