feat(status): mirror topic into tmux status bar

set-topic.sh now renames the tmux session to the project part of the
topic and stores the full topic in @claude_topic when run inside tmux.
Pairs with ~/.tmux.conf status-right showing #{@claude_topic}.

Claude-Session: https://claude.ai/code/session_01Xt2b3uQtakYGhH5Y653vwd

scripts/set-topic.sh

@@ -11,6 +11,16 @@ TOPIC="$*"
 HASH=$(echo -n "$CWD" | md5sum | cut -d' ' -f1)
 SESSION_FILE="/tmp/claude-session-id-$HASH"
 
+# If running inside tmux, mirror the topic into the tmux status bar:
+# session name = project part (before ':'), @claude_topic = full topic.
+if [[ -n "${TMUX:-}" ]]; then
+    PROJECT="${TOPIC%%:*}"
+    # tmux session names may not contain ':' or '.'
+    PROJECT=$(echo "$PROJECT" | tr ':.' '--' | cut -c1-30)
+    tmux rename-session "$PROJECT" 2>/dev/null || true
+    tmux set -q @claude_topic "$TOPIC" 2>/dev/null || true
+fi
+
 if [[ ! -f "$SESSION_FILE" ]]; then
     # Session ID file doesn't exist yet — the statusline hook hasn't run.
     # Write the topic to a pending file so statusline.sh can pick it up