1.6.0 — OpenCode free-model chain + model config

• OpenCode fallback is now a chain through every free model, not one spare, and
  it advances on a timeout too — not only on an empty answer. A dead free model
  no longer sinks the whole review.
• ~/.config/multi/models — pin your own OpenCode models by hand (opencode: <primary> <fallbacks…>), no agent needed. Overrides auto-detection; absent
  file keeps the free default.
• /multi:setup now warns loudly when you're on free models and offers to
  research current models, prices and usage for you, then writes your pick.
• Codex gets its own timeout (MULTI_CODEX_TIMEOUT, default 600s): high-effort
  runs stop dying at the shared 300s; review runs keep their longer budget.
• OpenCode error events are no longer swallowed — a failed run says why it was
  empty instead of "it ran but said nothing".
• Gemini stderr now lands in .dead.log on failure instead of vanishing.