- ds4: configurable janitor that age-prunes the on-disk KV-checkpoint cache
  (--kv-disk-dir, defaulted to <offload>/ds4-kv). New Ds4Config fields
  kv_cache_cleanup_enabled / kv_cache_max_age_hours (7d) /
  kv_cache_cleanup_interval_minutes (6h); new codai/api/ds4_kv_janitor.py
  reuses the tmp_janitor sweep (newest-mtime, so active sessions are spared),
  started from main.py only when ds4 + cleanup are both on. Settings UI +
  get/save wired.
- ds4: corrected the perf note — i-quants (IQ2/IQ3) and Q2_K load but fail
  ds4's CUDA prefill (gpu layer 0 ffn batch encode failed → empty reply);
  use K-quants Q4_K and up.
- models: pressing Enter in the HuggingFace search field now runs the search.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>