Add SessionStop hook and session-events.tsv duration tracking

- session-audit.json: add SessionStop entry pointing to new end-of-session scripts
- report-hook-event-end.sh/.ps1: log payload to hook-events.log and write TSV row to session-events.tsv
- report-hook-event.sh/.ps1: also write SessionStart TSV row to session-events.tsv so start/end pairs are queryable for duration

resources/scripts/report-hook-event-end.sh

@@ -0,0 +1,14 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+state_dir="${COPILOT_RESOURCES_STATE_DIR:-$HOME/.copilot-resources-state}"
+mkdir -p -- "$state_dir"
+
+event_payload="$(cat)"
+printf '%s\n' "$event_payload" >> "$state_dir/hook-events.log"
+
+# Append a TSV row to session-events.tsv for duration tracking.
+printf '%s\tSessionEnd\n' "$(date -u +"%Y-%m-%dT%H:%M:%SZ")" >> "$state_dir/session-events.tsv"
+
+printf '{"continue": true}\n'