docs: add PR review steering guide

[chaodu-agent]

Background

During PR #210, @the3mi demonstrated an excellent review style using severity levels (🔴🟡🟢) with concrete fix suggestions. This was effective enough that we want to codify it as a team standard.

What's added

docs/steering/pr-review.md — covers:

• Severity levels: 🔴 Critical (must fix) / 🟡 Minor (should fix) / 🟢 Info (no action)
• Comment format: what's wrong → where → why it matters → fix (with code)
• Self-review checklist: API docs checked, safety checks preserved, style consistent, tests correct
• Review etiquette: be specific, classify severity, batch feedback in one pass

Example

Uses the actual aspect ratio bug from PR #210 as the reference example.

Credit to @the3mi for the review format 🦞

[the3mi]

PR Review: docs/steering/pr-review.md

Overall: 🟢 Suggest Merge — solid contribution, two optional improvements noted below.

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🟡 Minor: Zero-width space in code fence (line ~52)

The example block has a U+200B zero-width space before the backticks:

```rust

This may render fine on GitHub but can break in other Markdown renderers (GitBook, Notion, etc.). Just remove the invisible character so it is a clean ```rust.

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🟡 Minor: Framework Q3 may not be actionable for AI agents

3. What alternatives were considered — find rejected alternatives from PR description, discussion, or commit history...

As an AI reviewer, I typically only have the PR own context. Without explicit mention in the PR description, I cannot discover rejected alternatives from commit history.

Suggested tweak: reframe as an author-facing responsibility — "Did the author explain why this approach was chosen over alternatives in the PR description?" This puts the burden on the PR author rather than the reviewer.

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🟢 Info: Everything else looks great

The severity levels (🔴🟡🟢), the four-question framework, and the self-review checklist are all clear and actionable. Good work codifying the team review culture!