Unifies user-visible copy on "Webhook" (routes and URLs unchanged), drops
the placeholder Profile settings section, and adds a copy-to-clipboard
affordance for the entrypoint URL as progressive enhancement — the button
stays hidden unless both the target element and the Clipboard API resolve,
so no dead control appears without JavaScript and the URL stays selectable.
Retention copy now matches what the code does: deletion is permanent, 0
retains forever, and a blank field means the default on create or the
current value on edit. The permanent-deletion sentence is suppressed for a
retain-forever webhook, which the reaper exempts before computing a cutoff.
Template tests gained a render-completed assertion. Without it, a page that
aborted mid-render still satisfied assertions matching the already-flushed
prefix, because renderTemplate streams to the ResponseWriter (#123).
Rewrites retention_days=0 to the RetentionForeverDays sentinel (365 * 1000)
in Webhook.BeforeSave, so the GORM column default cannot win the race. The
reaper skips retain-forever webhooks before building any query.
Also bounds the reaper's cutoff arithmetic: a time.Duration is int64
nanoseconds, so day counts above MaxFiniteRetentionDays (106751) overflowed
and wrapped the cutoff into the future, where created_at < cutoff matched
every row and the sweep deleted everything. parseRetentionDays now rejects
finite values above the ceiling, and retentionCutoff saturates so rows
written by older versions cannot reach it either.
Views render RetentionLabel() rather than the raw sentinel.
