feat(telemetry): add local agent efficiency metrics

shared/hooks/scripts/Record-Compact.ps1

@@ -2,7 +2,11 @@
 param()
 $root = Split-Path (Split-Path $PSScriptRoot -Parent) -Parent
 $stateDir = Join-Path $root '.ai-session'
-New-Item $stateDir -ItemType Directory -Force | Out-Null
-('{"event":"compact","timestamp":"' + (Get-Date).ToUniversalTime().ToString('o') + '"}') | Add-Content (Join-Path $stateDir 'telemetry.jsonl')
+if ($env:AI_CONFIG_TELEMETRY -ne '0') {
+    New-Item $stateDir -ItemType Directory -Force | Out-Null
+    $path = Join-Path $stateDir 'telemetry.jsonl'
+    ('{"event":"compact","timestamp":"' + (Get-Date).ToUniversalTime().ToString('o') + '"}') | Add-Content $path
+    if ((Get-Item $path).Length -gt 1048576) { Move-Item $path ($path + '.1') -Force }
+}
 & python (Join-Path $PSScriptRoot 'session-state.py') --hook
 exit $LASTEXITCODE