feat: global notification policy severity to channels (notif-22)

Singleton notification_policy table, NOTIFY_MIN_SEVERITY/CHANNELS env,
central dispatch gate, Settings policy UI, migration 007.

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

backend/app/services/telegram_notify.py

@@ -4,12 +4,11 @@ import httpx
 from sqlalchemy.orm import Session
 
 from app.models import Event, Problem
+from app.services.notification_severity import severity_meets_minimum
 from app.services.notification_settings import TelegramConfig, get_effective_telegram_config
 
 logger = logging.getLogger(__name__)
 
-SEVERITY_ORDER = {"info": 10, "warning": 20, "high": 30, "critical": 40}
-
 
 class TelegramNotConfiguredError(Exception):
     """Telegram disabled or missing token/chat_id."""
@@ -21,10 +20,6 @@ class TelegramSendError(Exception):
         self.status_code = status_code
 
 
-def _severity_value(value: str) -> int:
-    return SEVERITY_ORDER.get(value, 0)
-
-
 def send_telegram_text(message: str, *, config: TelegramConfig | None = None, force: bool = False) -> None:
     cfg = config or get_effective_telegram_config()
     if not force and not cfg.active:
@@ -61,14 +56,11 @@ def send_telegram_test_message(*, config: TelegramConfig | None = None) -> None:
     )
 
 
-def _should_notify_severity(severity: str, *, config: TelegramConfig) -> bool:
-    min_level = _severity_value(config.min_severity)
-    return _severity_value(severity) >= min_level
-
-
-def notify_event(event: Event, *, db: Session | None = None) -> None:
+def notify_event(event: Event, *, db: Session | None = None, apply_policy_gate: bool = True) -> None:
     cfg = get_effective_telegram_config(db)
-    if not cfg.active or not _should_notify_severity(event.severity, config=cfg):
+    if not cfg.active:
+        return
+    if apply_policy_gate and not severity_meets_minimum(event.severity, cfg.min_severity):
         return
     host = event.host.hostname if event.host else "unknown"
     message = (
@@ -85,9 +77,11 @@ def notify_event(event: Event, *, db: Session | None = None) -> None:
         logger.exception("notify_event telegram failed event_id=%s", event.event_id)
 
 
-def notify_problem(problem: Problem, event: Event | None = None, *, db: Session | None = None) -> None:
+def notify_problem(problem: Problem, event: Event | None = None, *, db: Session | None = None, apply_policy_gate: bool = True) -> None:
     cfg = get_effective_telegram_config(db)
-    if not cfg.active or not _should_notify_severity(problem.severity, config=cfg):
+    if not cfg.active:
+        return
+    if apply_policy_gate and not severity_meets_minimum(problem.severity, cfg.min_severity):
         return
     host = problem.host.hostname if problem.host else "unknown"
     related = ""