report the working directory to the terminal with OSC 7

Before each prompt gosh sends ESC ] 7 ; file://host/path BEL (host and
path percent-encoded), so terminals like GNOME Terminal open new tabs
and windows in the directory of the shell instead of the one gosh was
started in. Nothing is sent if stdout is not a terminal or TERM=dumb.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

README.md

@@ -59,6 +59,8 @@ Features:
     GOSH_COLORS='user=1;33:path=36' (keys user, root, path, error; values
     are ANSI SGR codes, empty = no color); disabled with $NO_COLOR,
     TERM=dumb or when output is not a terminal
+  - Reports the working directory to the terminal (OSC 7) before each
+    prompt, so new tabs/windows open in the same directory
   - Variables: name=value sets a variable (like set), name=value command
     sets it only for that command; the value is not split or expanded as
     a pattern