On resource-contended hosts the embedded Hindsight daemon can exceed a
single 2s /health check; upstream then waits a grace window before
treating it as stale and killing+restarting it (hindsight-embed reads
HINDSIGHT_EMBED_PORT_HEALTH_GRACE_TIMEOUT, default 30s, into a
module-level constant at import time). Users on busy boxes had no
Hermes-side way to raise it short of hand-setting an env var.
Add a 'port_health_grace_timeout' config.json option to the Hindsight
plugin. When set, initialize() exports it to the process env BEFORE
daemon_embed_manager is imported (the import-time read is the contract).
setdefault() so an explicit operator env override always wins. Exposed
in 'hermes memory setup' for local_embedded mode.
Follow-up to #50308 / issue #13125 comment thread.
