Feature: consult command for persistent multi-turn Q&A sessions

Problem

The current commands are all single-shot: review, adversarial-review, rescue. There's no way to have an ongoing conversation with Codex about a topic -- exploring a design, asking follow-up questions, iterating on an approach -- while maintaining context across turns.

The plugin already has thread management infrastructure (thread/start, thread/resume). Exposing this as a user-facing command would unlock conversational use cases.

Proposal

Add /codex:consult [topic] command:

• Starts a new Codex thread scoped to the current repo
• Subsequent /codex:consult [follow-up] resumes the same thread
• --fresh flag starts a new thread (discards previous context)
• Session mapping persisted per-repo so threads survive across commands
• No structured verdict required -- response presented verbatim

Use cases:

• "How does the auth middleware work in this repo?" -> follow-up: "What would break if we replaced it with JWT?"
• Iterating on a design: ask, get feedback, refine, ask again
• Exploring unfamiliar code with a knowledgeable companion

Implementation notes

The broker already supports thread/start and thread/resume. This would be a new command definition + prompt template + session state tracking (repo path -> thread ID mapping).

Start by tracing the existing command definitions and the broker's thread/start and thread/resume entry points. Then inspect how prompt templates and repo-scoped state are handled. Done means /codex:consult supports new and follow-up prompts, --fresh resets the session, and the thread mapping persists per repository.