Record selection accessibility review lesson

[mchwang]

PR #14's automated review caught a reusable accessibility gap: a row could look selected while assistive technology received no selected-state signal. The lesson should have been included before PR #14 merged.

Add two repository rules:

• Stateful rows and controls must expose visual selection through the appropriate accessibility attribute and test that state across navigation.
• Review-lesson extraction is an explicit merge gate. Every review finding must be classified in the PR body as covered by an existing cited rule, captured by a new cited rule in the reviewed head, or one-off with a recorded reason. Merge is prohibited until the audit is complete.

Review-lesson audit

• PR Preserve composer drafts during Refresh #14 finding, “Expose selected state for retained-draft rows”: captured by the new rule under Async review UI in this branch.
• PR Record selection accessibility review lesson #15 review round 1: no findings.
• No findings were classified as one-off or declined.

Validation: git diff --check passes. CI reruns the repository's typecheck, 188 unit/integration tests, and 38 browser tests on the updated head. Copilot rereview is requested after this update.

[Copilot]

Copilot review overview

🟢 Approval recommended

The documentation change has no unresolved blocking issues.

Review effort: Lite
Findings: None

What changed in this PR

Adds a repository accessibility guideline for selected-state semantics and navigation testing.

Changes:

• Documents appropriate aria-current/aria-selected usage.
• Requires regression coverage across navigation.

File	Description
AGENTS.md	Adds the selected-state accessibility and testing rule.

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[Copilot]

Copilot review overview

🟢 Approval recommended

The documentation-only change has been fully reviewed with no unresolved blocking issues.

Review effort: Lite
Findings: None