docs(mappers): time no longer dates detection

Eight mappers (Cortex XDR, CrowdStrike, Rapid7) still called the OCSF
`time` field "the MTTD anchor" that Riposte reads to stamp detected_at.
Riposte retired MTTD in migration 0256 and stamps detection at
ingestion for every alert; the mappings stay, as the alert's own record
of when the source saw the event. Comments only: no mapping changes.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

integrations/rapid7-insightidr/mappers/search_alerts.yaml

@@ -50,7 +50,9 @@ ocsf:
   - { source_path: "type",                    ocsf_field: "finding_info.analytic.name" }
   - { source_path: "rule.rrn",                ocsf_field: "finding_info.analytic.uid" }
   - { source_path: "rule.version_rrn",        ocsf_field: "finding_info.analytic.version" }
-  # ── Detection time: the MTTD anchor ───────────────────────────────
+  # ── Event time (OCSF `time`) ───────────────────────────────────────
+  # Riposte no longer reads it to date detection (MTTD retired, migration 0256):
+  # it is the alert's own record of when the source saw the event.
   # alerted_at is when the underlying event happened in the source system; created_at is
   # when Rapid7 finished building the alert. Weakest first, strongest last.
   - { source_path: "created_at",              ocsf_field: "time" }