feat: report scheduler - webhook auto resolve

[hoalongnatsu]

Scheduled incident report + timezone

Added schedule_enabled, send_time ("HH:MM", 24h), timezone ("UTC"/IANA)
to the report settings table.

New Scheduled daily delivery section: daily send at send_time in
timezone, reusing default_window (window ends at send time) and
default_channel; timezone also controls the report's printed timestamps
(previously UTC-only); schedule gated on the report being enabled; UTC vs
Local-time UI note; HA note (exactly one replica sends the digest).

Added two edge-case bullets (feature off → no send; schedule on/report off →
no send).

Verified against pkg/services/reportsettings.go (defaults: schedule off,
send_time "09:00", timezone "UTC").

Webhook auto resolve

The product decision for webhook auto-resolve changed: auto-resolve must now
ONLY stamp the incident resolved in backend storage. It must NOT disable or
skip the on-call escalation or the ack (AckURL) path. Default stays ON.

Previously CreateIncident treated an auto-resolved webhook incident like a
resolved-from-payload one: it computed finalResolved = resolved || autoResolve
and used that single flag to gate BOTH AckURL injection and on-call escalation,
so an auto-resolved incident got no ack URL and no on-call. That "skip ack +
skip on-call" behaviour is removed.