Add alert triage suppression context gates

[Errordog2]

Summary

• Adds a suppression and stale-context confidence gate to alert-triage.
• Requires raw event count, unique entities, first/last-seen windows, suppression owner/expiry/approval, and asset/identity enrichment freshness before downgrading or closing grouped alerts.
• Adds queue saturation and uncertainty escalation guidance, plus output fields for suppression/context confidence.

Addresses #2547.

Validation

• git diff --check
• Markdown fence balance check
• Targeted marker check for v1.0.1, suppression/deduplication evidence, context freshness, queue saturation, and output fields