feat(session): maintain canonical task state

shared/hooks/scripts/Show-SessionStatePointer.ps1

@@ -1,4 +1,4 @@
 [CmdletBinding()]
 param()
-$root = Split-Path (Split-Path $PSScriptRoot -Parent) -Parent
-if (Test-Path (Join-Path $root '.ai-session/state.json')) { Write-Output 'Task state is available in .ai-session/state.json; read it only if needed.' }
+& python (Join-Path $PSScriptRoot 'session-state.py') --hook
+exit $LASTEXITCODE