Improve timestamp handling and event navigation

server/monlet_server/settings.py

@@ -1,6 +1,8 @@
 from pydantic import field_validator
 from pydantic_settings import BaseSettings, SettingsConfigDict
 
+from .timeutil import validate_time_zone
+
 
 class Settings(BaseSettings):
     model_config = SettingsConfigDict(env_prefix="MONLET_", env_file=".env", extra="ignore")
@@ -25,6 +27,7 @@ class Settings(BaseSettings):
     notifier_max_attempts: int = 8
     notifier_lease_sec: int = 300
     notifier_http_timeout_sec: float = 10.0
+    notification_time_zone: str = "UTC"
 
     notifier_debug_enabled: bool = True
     notifier_telegram_enabled: bool = False
@@ -43,6 +46,11 @@ class Settings(BaseSettings):
             raise ValueError("MONLET_AUTH_TOKEN must be set to a non-default value")
         return value
 
+    @field_validator("notification_time_zone")
+    @classmethod
+    def _validate_notification_time_zone(cls, value: str) -> str:
+        return validate_time_zone(value)
+
     @property
     def enabled_notifiers(self) -> list[str]:
         out: list[str] = []