Remove no-tool goal continuation suppression

[etraut-openai]

Why

/goal is supposed to keep Codex working until the goal is actually done. The previous continuation logic had two ways to stop early: the continuation prompt told the model to wait for new input when it felt blocked, and the runtime suppressed another continuation turn after a continuation finished without any tool calls.

That made goals stop short even when the agent could still keep making progress (I received a few reports of this from users). It also relied on a brittle heuristic that treated "no registry tool calls" as equivalent to "should stop."

What changed

• removed the continuation prompt sentence that told the model to stop and wait for new input when it could not continue productively
• removed the goal runtime suppression heuristic that stopped auto-continuation after a no-tool continuation turn
• deleted the continuation-activity bookkeeping and left tool_calls as telemetry only
• added focused regressions for the two intended behaviors: completed no-tool continuation turns still continue, while request_user_input keeps the existing turn open instead of spawning a new continuation