feat(omo): coloured tab markers and clickable Ghostty banners

omo-notify now drives three signals from omo's UserPromptSubmit, Stop
and Notification hooks:

- A sound through afplay, so Focus modes cannot mute it
- A Ghostty notification (OSC 777) written to the session's tmux client
  terminal, so clicking it opens the tab it came from. This replaces the
  osascript banner, which opened Script Editor's file picker on click
- omo-status markers in front of the tab title: red error, amber
  waiting for input, green finished, blue working. A tab shows its most
  urgent agent; focusing it clears red, amber and green and selects the
  pane that sent the banner

tmux puts @omo_status in the title and runs omo-status on client focus.

.local/bin/omo-status

@@ -0,0 +1,88 @@
+#!/usr/bin/env bash
+# Coloured attention markers on Ghostty tabs for omo sessions. tmux puts the
+# session's @omo_status in front of the tab title (set-titles-string in
+# ~/.tmux.conf), so each tab shows what its agents need:
+#   🔴 stopped with an error   🟡 waiting for your answer
+#   🟢 finished                🔵 working
+# Each pane running omo keeps its own state in the pane option @omo_state, and
+# the tab shows the most urgent one. Focusing the tab clears red, amber and green,
+# and selects the pane whose banner you were sent (@omo_jump, set by omo-notify).
+#
+# Usage: omo-status set <pane> <working|input|done|error|clear>
+#        omo-status focus <client>     (run by the tmux client-focus-in hook)
+
+export PATH="/opt/homebrew/bin:/usr/local/bin:/usr/bin:/bin:$PATH"
+
+icon() {
+  case $1 in
+    error) echo "🔴" ;;
+    input) echo "🟡" ;;
+    done) echo "🟢" ;;
+    working) echo "🔵" ;;
+  esac
+}
+
+rank() {
+  case $1 in
+    error) echo 4 ;;
+    input) echo 3 ;;
+    done) echo 2 ;;
+    working) echo 1 ;;
+    *) echo 0 ;;
+  esac
+}
+
+show_most_urgent() {
+  local session=$1 state best=""
+  while read -r state; do
+    if (($(rank "$state") > $(rank "$best"))); then best=$state; fi
+  done < <(tmux list-panes -s -t "$session" -F '#{@omo_state}')
+  if [[ -n $best ]]; then
+    tmux set-option -t "$session" @omo_status "$(icon "$best")"
+  else
+    tmux set-option -u -t "$session" @omo_status
+  fi
+}
+
+# You are looking at a pane when its tab has focus and its window is showing.
+looking_at() {
+  local pane=$1 session=$2
+  [[ $(tmux display-message -p -t "$pane" '#{window_active}') == 1 ]] &&
+    tmux list-clients -t "$session" -F '#{client_flags}' | grep -q focused
+}
+
+case ${1:-} in
+  set)
+    pane=${2:?pane id required} state=${3:?state required}
+    session=$(tmux display-message -p -t "$pane" '#{session_id}' 2>/dev/null) || exit 0
+    if [[ $state != working && $state != clear ]] && looking_at "$pane" "$session"; then
+      state=clear
+    fi
+    if [[ $state == clear ]]; then
+      tmux set-option -p -u -t "$pane" @omo_state
+    else
+      tmux set-option -p -t "$pane" @omo_state "$state"
+    fi
+    show_most_urgent "$session"
+    ;;
+  focus)
+    client=${2:?client required}
+    session=$(tmux list-clients -F '#{client_name} #{session_id}' | awk -v c="$client" '$1 == c { print $2 }')
+    [[ -n $session ]] || exit 0
+    jump=$(tmux show-option -qv -t "$session" @omo_jump)
+    if [[ -n $jump ]]; then
+      tmux set-option -u -t "$session" @omo_jump
+      tmux select-window -t "$jump" \; select-pane -t "$jump" 2>/dev/null
+    fi
+    while read -r pane state; do
+      case $state in
+        input | done | error) tmux set-option -p -u -t "$pane" @omo_state ;;
+      esac
+    done < <(tmux list-panes -s -t "$session" -F '#{pane_id} #{@omo_state}')
+    show_most_urgent "$session"
+    ;;
+  *)
+    sed -n '2,/^$/s/^# \{0,1\}//p' "$0" >&2
+    exit 2
+    ;;
+esac