Release nspawn-vault-v1.0.0-11

nspawn-vault v1.0.0-11

Adds email as a third dead-man's-switch alert channel, alongside the
existing Pushover and Slack alerts. Pushover/Slack stay exactly as they
were (one shared config for the whole vault); email adds per-source-host
recipients against a single shared SMTP relay, since a large fleet needs
different people notified about different source hosts, not one global
recipient list.

• New SMTP_HOST / SMTP_PORT / SMTP_TLS_MODE / SMTP_USER / SMTP_PASS
  / SMTP_FROM keys in notify.conf (STARTTLS on 587 or implicit TLS on
  465, both configurable).
• New per-host recipients file: /etc/nspawn-vault/<host>/notify-email,
  one address per line.
• New usr/libexec/nspawn-vault/send-email.sh, a curl-based SMTP sender
  shared by check-stale.sh and nspawn-vault-web's new "send test email"
  admin button.
• check-stale.sh now loops configured hosts/containers instead of
  globbing state files directly - needed to know which host a container
  belongs to (the state filename alone can't be split back into an
  unambiguous host/container pair). Existing per-container Pushover/Slack
  alerts are unchanged; email is batched one message per host listing
  every problem container, instead of one email per container, to avoid
  flooding recipients across a large fleet.

Why

Built for a fleet of roughly 200 source hosts. A single flat alert
recipient list stops working at that scale - different teams/people care
about different hosts, and email is the lowest common denominator every
admin can receive without extra setup.

Verified live

Ran the rewritten check-stale.sh against real production config and
state data on nspawn-vault.vpn.fhd.se (besten.alsike.minten.se,
knorrhane2.alsike.minten.se) - identical OK/ALERT results to before the
rewrite. Also live-tested the shell-quoting on the new SMTP_PASS field
with a $()/backtick injection payload (same class of protection as the
existing Pushover/Slack secrets) - confirmed inert.