fix: ds4 kv-janitor loop var shadowed `import threading as _t`

The --kv-disk-dir parse loop used `for _i, _t in ...`, making `_t` a local
in main() and shadowing the module-level `import threading as _t`, so the
later `_t.Thread(...)` raised UnboundLocalError and crash-looped both
engines. Renamed the loop var to `_tok`.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

codai/main.py

@@ -365,8 +365,8 @@ def main():
             if "--kv-disk-dir" in _extra:
                 import shlex as _shlex
                 _toks = _shlex.split(_extra)
-                for _i, _t in enumerate(_toks):
-                    if _t == "--kv-disk-dir" and _i + 1 < len(_toks):
+                for _i, _tok in enumerate(_toks):
+                    if _tok == "--kv-disk-dir" and _i + 1 < len(_toks):
                         _kv_dir = _toks[_i + 1]
                         break
             if not _kv_dir: