cli: Remove unreachable input guard

Backup creation rejects a noninteractive terminal before this branch, so the later stdin.isatty() rejection can never run. Removing it preserves the interactive behavior and leaves the integrated source under its strict review line budget. Refs #46 and #81.

Author: Codex Agent

src/codex32/cli.py

@@ -490,8 +490,6 @@ def _create(
             raise _UsageError("For thresholds 4 through 9, choose --shares or --indices.")
     core = _connected_core()
     source = _creation_source(profile) if existing else None
-    if not existing and not sys.stdin.isatty() and _text("", optional=True):
-        raise _UsageError("Use --existing when supplying a seed or secret.")
     if isinstance(source, (Share, Secret)) and not isinstance(source, MasterSeed):
         raise _UsageError(f"Enter one {_profile_rules(profile).label}, not a share or another backup type.")
     try: