Consolidate fail2ban truthy values into shared constants

backend/app/utils/constants.py

@@ -16,6 +16,9 @@ DEFAULT_FAIL2BAN_SOCKET: Final[str] = "/var/run/fail2ban/fail2ban.sock"
 FAIL2BAN_SOCKET_TIMEOUT_SECONDS: Final[float] = 5.0
 """Maximum seconds to wait for a response from the fail2ban socket."""
 
+FAIL2BAN_TRUTHY_VALUES: Final[frozenset[str]] = frozenset({"true", "yes", "1"})
+"""String values treated as boolean true by fail2ban configuration parsers."""
+
 # ---------------------------------------------------------------------------
 # Database
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