feat: live последние события на Dashboard; retention, health, runbook

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/app/services/retention.py

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+"""Удаление устаревших events и resolved problems."""
+
+from datetime import datetime, timedelta, timezone
+
+from sqlalchemy import delete
+from sqlalchemy.orm import Session
+
+from app.config import Settings
+from app.models import Event, Problem
+
+
+def purge_old_data(db: Session, settings: Settings) -> dict:
+    """
+    Events: received_at старше sac_events_retention_days.
+    Problems: status=resolved и updated_at старше sac_problems_retention_days.
+    """
+    now = datetime.now(timezone.utc)
+    events_cutoff = now - timedelta(days=settings.sac_events_retention_days)
+    problems_cutoff = now - timedelta(days=settings.sac_problems_retention_days)
+
+    events_result = db.execute(delete(Event).where(Event.received_at < events_cutoff))
+    events_deleted = events_result.rowcount or 0
+
+    problems_result = db.execute(
+        delete(Problem).where(
+            Problem.status == "resolved",
+            Problem.updated_at < problems_cutoff,
+        )
+    )
+    problems_deleted = problems_result.rowcount or 0
+
+    db.commit()
+
+    return {
+        "events_deleted": events_deleted,
+        "problems_deleted": problems_deleted,
+        "events_cutoff": events_cutoff.isoformat(),
+        "problems_cutoff": problems_cutoff.isoformat(),
+    }