Display selected model in review output

[wesm]

Summary

When a model is explicitly configured (via --model flag or config), display it in the review output so users can see which model was used.

Current Behavior

Review (by claude-code)
------------------------------------------------------------
{review output}

Proposed Behavior

Review (by claude-code)              # model empty/default - no change
Review (by claude-code, gpt-4)       # model explicitly set

Implementation

The Review struct doesn't currently have a Model field - the model is stored on ReviewJob. Options:

1. Add Model as a joined field on Review - populate when fetching from DB/API (similar to how Verdict is computed)
2. Include in showReview() display when non-empty

Context

This follows up on PR #126 which added --model support to all agents. The model is stored in the database and visible in job listings (roborev jobs), but not shown in the review output itself.

Files to modify

• internal/storage/models.go - add Model field to Review struct
• internal/storage/reviews.go - populate Model when fetching reviews (join with review_jobs)
• cmd/roborev/main.go - update showReview() to display model when non-empty
• cmd/roborev/run.go - update showPromptResult() similarly