feat: add nowcast point alarm unregister client with confirmation and backup

Shows environment, count and an irreversibility warning, requires typing the confirmation word (plus the environment name on prod), backs every registration up through get-by-id before deleting and aborts the whole run if the backup cannot be completed.

common/config.py

@@ -68,6 +68,7 @@ class Settings:
     token_expiry_skew_seconds: int
     max_retries: int
     retry_base_seconds: float
+    environment: str = ""
 
     @classmethod
     def from_env(cls, env_file: Path = DEFAULT_ENV_FILE) -> "Settings":
@@ -96,6 +97,7 @@ class Settings:
         return cls(
             env_file=env_file,
             base_url=base_url,
+            environment=environment,
             hmac_secret=_required("IKLIM_HMAC_SECRET"),
             accept_language=language,
             timeout_seconds=_positive_float("IKLIM_TIMEOUT_SECONDS", "30"),