Expose every live notifications.* server setting on a new admin
Notifications tab (next to Email): kill switches, fanout tuning,
webhook guards, and retention. Unset kill switches render as enabled
to match the backend defaults, numeric fields surface their effective
defaults, and enabling private webhook destinations shows an SSRF
warning. v1.5 roadmap item 1; no backend changes — all keys are
live-read.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
