refine: branch review uses fix agent instead of review agent

[tlmaloney]

Summary

roborev refine passes the refine/fix agent to the branch review enqueue call, causing the server to use the wrong agent for the review step.

Root Cause

In cmd/roborev/refine.go, the branch review is enqueued with resolvedAgent (resolved via the "refine" workflow):

resolvedAgent := config.ResolveAgentForWorkflow(opts.agentName, repoPath, cfg, "refine", resolvedReasoning)
// ...
jobID, err = client.EnqueueReview(repoPath, rangeRef, resolvedAgent)

On the server side, ResolveAgentForWorkflow treats a non-empty cli argument as an explicit override and returns it immediately, bypassing the workflow-specific config:

func ResolveAgentForWorkflow(cli, repoPath string, globalCfg *Config, workflow, level string) string {
    if s := strings.TrimSpace(cli); s != "" {
        return s  // short-circuits — never consults review_agent config
    }
    // ...
}

The server resolves the agent via the "review" workflow but receives "claude-code" (the refine agent) as the cli argument, so review_agent config is ignored. However, the model is resolved via the "review" workflow, picking up review_model. This creates a mismatch — e.g., claude-code paired with gpt-5.4.

Reproduction

Config:

review_agent = 'codex'
review_model = 'gpt-5.4'
refine_agent = 'claude-code'
refine_model = 'claude-opus-4-6'

Run roborev refine on a feature branch. The branch review job fails with:

agent: claude-code failed
stream: stream errors: There's an issue with the selected model (gpt-5.4).

Fix

Pass empty string for the agent in the branch review enqueue call so the server resolves it via the "review" workflow config:

jobID, err = client.EnqueueReview(repoPath, rangeRef, "")