Widen the allow_session tier from Matrix to every adapter the gateway
notifies: Telegram, Discord, Slack, Feishu, and Teams gate their Session
button on it; WhatsApp Cloud and qqbot accept the kwarg (no session tier
in their button sets). Also thread allow_session through the plugin-
escalation gate, the execute_code guard payload, and the plain-text
fallback so every notify path carries the same capability flags.