fix: make auto-continuation settings-only

[Brian Krabach (bkrabach)]

What changed

Remove the auto_continue field from the interactive OpenAI provider setup wizard and document it as a settings-only option. It still defaults to true; manually setting auto_continue: false disables automatic continuation, and the per-call override remains supported.

Why

This option controls bounded output behavior and additional paid continuation requests, so it should remain an explicit advanced configuration choice rather than a routine setup prompt. The companion CLI change that preserves explicit settings during provider reconfiguration is merged in #366.

How to verify

• OpenAI offline suite: 1,409 passed.
• Installed-package acceptance across CLI, OpenAI, and vLLM: 50 cases passed, including wizard prompts, default/opt-out behavior, and settings preservation. No live inference was used.
• GitHub Actions runs the repository CI suite on Python 3.11 and 3.12.

Breaking changes

None. Runtime behavior and the default remain unchanged; only the wizard prompt is removed.