fix: host_silence proactive notify when event is None

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

backend/tests/test_telegram_templates.py

@@ -326,3 +326,32 @@ def test_agent_inventory_hardware_change_template():
     assert "железо" in text.lower() or "Изменилось" in text
     assert "memory_gb" in text
     assert "32" in text
+
+
+def test_format_problem_host_silence_scan_without_event():
+    from app.models import Host, Problem
+    from app.services.problem_rules import RULE_HOST_SILENCE
+    from app.services.telegram_templates import format_problem_telegram_html
+
+    host = Host(
+        hostname="YURKOV-PC",
+        os_family="windows",
+        product="rdp-login-monitor",
+        last_seen_at=datetime(2026, 6, 11, 9, 0, tzinfo=timezone.utc),
+    )
+    problem = Problem(
+        host_id=1,
+        host=host,
+        title="Host silence: YURKOV-PC",
+        summary="Нет свежего agent.heartbeat более 300 мин",
+        severity="high",
+        status="open",
+        rule_id=RULE_HOST_SILENCE,
+        fingerprint="fp-silence",
+        event_count=0,
+        last_seen_at=datetime(2026, 6, 11, 9, 0, tzinfo=timezone.utc),
+    )
+    text = format_problem_telegram_html(problem, event=None)
+    assert "периодическая проверка SAC" in text
+    assert "host_silence scan" in text
+    assert "YURKOV-PC" in text or "UNMS" not in text  # host label uses hostname