otaku 0.1.2

Hardening release: complete state-dir isolation, never-overwrite key handling, and REPL quality-of-life.

Fixed

• OTAKU_CONFIG_DIR is now fully isolated. Previously a custom state dir
  wrote a config pointing at the default ~/.otaku/history.db, and — much
  worse — its first run replaced the shared OS-keychain key, making the
  primary setup's history permanently undecryptable. Each dir now gets its own
  default database and its own keychain item; the default ~/.otaku keeps the
  legacy item name, so existing installs keep unlocking.
• Unlock failures no longer stutter ("Could not unlock encryption key: could
  not unlock…") and a key mismatch is spelled out instead of surfacing as an
  empty error.
• /remember no longer risks dropping other models' saved defaults when
  model_defaults.json is corrupt — it refuses instead, and writes atomically.

Changed

• Key setup never overwrites anything. Provisioning reuses an existing
  keychain or retrieve_command key instead of replacing it, keychain writes
  are add-only, and keys.json is created exclusively — so deleting
  keys.json no longer burns the key, and a restored backup keeps working.
  A stray pre-envelope history.key is left in place rather than deleted.
• Bare otaku unlocks encryption before the model picker, so interactive
  key ceremonies (passphrase, command providers) happen up front.
• /history rows fall back title → summary → first prompt.
• Config paths in notices are shown ~-shortened; shorter -nr banner.

Added

• /model remembers the switched-to model as the last used one (the picker
  preselects it next time).
• [defaults].verbose — set the stats line globally (a session-wide UI
  preference; deliberately not per-model, so /remember doesn't pin it).