feat: Telegram notifications from SAC on ingest

Send Telegram alerts for high/critical events and new Problems.
Configurable via TELEGRAM_* env vars; ingest never fails on send errors.

backend/app/config.py

@@ -45,6 +45,10 @@ class Settings(BaseSettings):
 
     event_schema_path: str = str(SCHEMA_PATH)
     cors_origins: str = "*"
+    telegram_enabled: bool = False
+    telegram_bot_token: str = ""
+    telegram_chat_id: str = ""
+    telegram_min_severity: str = "high"
 
 
 @lru_cache