Add <prefix>A binding to display-popup with agent.sh

Enables the use of AI agents (claude, gemini) in a persistent
display-popup, backed by a tmux session, via the <prefix>A binding.

agent.sh

@@ -0,0 +1,53 @@
+#!/usr/bin/env bash
+
+set -e
+
+# Check which agent commands are available
+agents=()
+command -v claude &>/dev/null && agents+=(claude)
+command -v gemini &>/dev/null && agents+=(gemini)
+
+if [ ${#agents[@]} -eq 0 ]; then
+  echo "No agent commands found (claude, gemini)"
+  exit 1
+fi
+
+# Use the current directory (set via display-popup -d)
+dir="${PWD:-$HOME}"
+# Use the directory basename as window name
+window_name=$dir
+
+# Create the agent session if it doesn't exist
+if ! tmux has-session -t agent; then
+  tmux new-session -ds agent -c "$dir" -n "$window_name" "${agents[0]}"
+  [ ${#agents[@]} -gt 1 ] && tmux split-window -h -t agent:0 "${agents[1]}"
+  # Store the directory in a window option for later matching
+  tmux set-window-option -t agent @agent_dir "$dir"
+  tmux set-option -t agent status off
+  tmux attach-session -t agent
+  exit 0
+fi
+
+# Search for an existing window with matching directory
+target_window=""
+for window_id in $(tmux list-windows -t agent -F '#{window_id}'); do
+  window_dir=$(tmux show-window-option -t "$window_id" -v @agent_dir 2>/dev/null || true)
+  if [ "$window_dir" = "$dir" ]; then
+    target_window="$window_id"
+    break
+  fi
+done
+
+if [ -n "$target_window" ]; then
+  # Select the existing window
+  tmux select-window -t "$target_window"
+else
+  # Create a new window with agents
+  tmux new-window -t agent -c "$dir" -n "$window_name" "${agents[0]}"
+  [ ${#agents[@]} -gt 1 ] && tmux split-window -h -t agent -c "$dir" "${agents[1]}"
+  # Store the directory in a window option for later matching
+  tmux set-window-option -t agent @agent_dir "$dir"
+fi
+
+# Attach to the session
+tmux attach-session -t agent