fix: add COLUMNS/LINES env var fallback in backend-size

When all ioctl methods return rows=0 (SBCL process context), try
/ from the shell environment. These are set by bash
and may survive SBCL's env filtering in some configurations.

src/backend/modern.lisp

@@ -205,6 +205,16 @@ as a fallback when a keyword is not in *named-colors*.")
                              (rows (sb-alien:deref winsize 0)))
                          (values cols rows)))))
               (sb-unix:unix-close tty-fd)))))
+      ;; $COLUMNS/$LINES env vars — set by bash, may be available
+      ;; even when ioctl fails (SBCL strips them in some contexts
+      ;; but not all).
+      (ignore-errors
+        (let* ((cstr (sb-ext:posix-getenv "COLUMNS"))
+               (rstr (sb-ext:posix-getenv "LINES"))
+               (cols (when cstr (parse-integer cstr :junk-allowed t)))
+               (rows (when rstr (parse-integer rstr :junk-allowed t))))
+          (when (and cols rows (> cols 0) (> rows 0))
+            (values cols rows))))
       (values 80 24)))
 
 (defmethod backend-write ((b modern-backend) string)

src/backend/simple.lisp

@@ -63,6 +63,14 @@
                                (sb-alien:deref winsize 0))))
                    (sb-alien:free-alien winsize))
                (sb-unix:unix-close tty-fd)))))
+      ;; $COLUMNS/$LINES env vars
+      (ignore-errors
+        (let* ((cstr (sb-ext:posix-getenv "COLUMNS"))
+               (rstr (sb-ext:posix-getenv "LINES"))
+               (cols (when cstr (parse-integer cstr :junk-allowed t)))
+               (rows (when rstr (parse-integer rstr :junk-allowed t))))
+          (when (and cols rows (> cols 0) (> rows 0))
+            (values cols rows))))
       (values 80 24)))
 
 (defmethod backend-write ((b simple-backend) string)