Uses getAll() instead of getAvailable() so stale models like grok-2
are caught even when the user has no auth for the correct provider yet.
Resets thinking to off when the configured model was invalid.
- Remove gsd-pi from its own dependencies (circular dep caused ENOTEMPTY install failures)
- Auto-select anthropic/claude-sonnet-4-6 as default model for new installs
- Reset to valid model if configured model no longer exists in registry
- Default thinking level to off
When users logged in via /login but never explicitly ran /model, the agent
would throw 'No model configured' on every action. Now GSD auto-selects
a default model from available authenticated providers on startup.
Preference order: claude-sonnet-4-20250514 > any Anthropic model > first available.
Also documented /model command in README Getting Started section.
Closes#4
