Replace the process-global HERMES_CRON_SESSION env var with a per-session
ContextVar so a cron tick in the gateway process cannot leak into unrelated
live gateway/API/TUI turns. The cron scheduler now sets the ContextVar
inside the job's try/finally scope and resets it on cleanup. Gateway, API
server, ACP adapter, and TUI gateway all pass cron_session='' to explicitly
mark their sessions as non-cron, masking any stale process env.
Co-authored-by: hinablue <hinablue@gmail.com>
Closes#37968
kshitij