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.ps1

@@ -0,0 +1,12 @@
+$ErrorActionPreference = 'Stop'
+
+$StateDir = if ($env:COPILOT_RESOURCES_STATE_DIR) { $env:COPILOT_RESOURCES_STATE_DIR } else { Join-Path $HOME '.copilot-resources-state' }
+New-Item -ItemType Directory -Path $StateDir -Force | Out-Null
+
+$Payload = [Console]::In.ReadToEnd()
+$Payload | Add-Content -LiteralPath (Join-Path $StateDir 'hook-events.log')
+
+# Append a TSV row to session-events.tsv for duration tracking.
+"$(Get-Date -AsUTC -Format o)`tSessionEnd" | Add-Content -LiteralPath (Join-Path $StateDir 'session-events.tsv')
+
+'{"continue": true}'