Fix clipboard OSC 52 fallback: walk past nvim's tty-less embed process

Nvim isn't a single process attached to the terminal: the process that
actually spawns jobs (clipboard-copy included) is a separate `nvim --embed`
core process with no tty of its own (ps shows `?`); the real pty belongs to
a distinct parent UI process. Checking only the immediate parent's tty (as
the previous fix did) found the embed process's `?` and fell through to the
broken /dev/tty path every time in real interactive use, even though it
looked fine in headless testing. Walk up the process tree past any tty-less
ancestors instead.

Verified against the real docker-compose path in actual (non-headless) TUI
mode, with real keystrokes fed through a pty: the OSC 52 sequence now
reaches the terminal with no error, where it previously still failed.

bin/clipboard-copy

@@ -20,11 +20,24 @@ else
     data=$(base64 | tr -d '\n')
     # /dev/tty needs this process's own session to have a controlling
     # terminal, but a job spawned by nvim's clipboard provider doesn't get
-    # one (nvim's job-spawning doesn't establish a ctty for children).
-    # Resolve the real terminal from the parent's (nvim's) recorded tty
-    # instead, which doesn't depend on this process having its own ctty.
-    real_tty="/dev/$(ps -o tty= -p "$PPID" 2>/dev/null | tr -d ' ')"
-    if [ -w "$real_tty" ]; then
+    # one (nvim's job-spawning doesn't establish a ctty for children). Nvim
+    # itself also isn't a single process: the one actually spawning jobs is
+    # a `nvim --embed` core process with no tty of its own (shown as `?` in
+    # ps) -- the real terminal belongs to a separate parent UI process. Walk
+    # up the process tree past any tty-less ancestors to find it.
+    real_tty=""
+    pid="$PPID"
+    i=0
+    while [ "$i" -lt 10 ] && [ -n "$pid" ] && [ "$pid" != "0" ]; do
+        t=$(ps -o tty= -p "$pid" 2>/dev/null | tr -d ' ')
+        if [ -n "$t" ] && [ "$t" != "?" ]; then
+            real_tty="/dev/$t"
+            break
+        fi
+        pid=$(ps -o ppid= -p "$pid" 2>/dev/null | tr -d ' ')
+        i=$((i + 1))
+    done
+    if [ -n "$real_tty" ] && [ -w "$real_tty" ]; then
         printf '\033]52;c;%s\a' "$data" > "$real_tty"
     else
         printf '\033]52;c;%s\a' "$data" > /dev/tty