fix(frontend): label icon-only workspace buttons

[seonghobae]

Summary

• Add localized aria-labels to icon-only Calendar and Tasks controls.
• Add page-level regression assertions for the accessible labels.
• Record the icon-only control accessibility anti-pattern in AGENTS.md.

Replaces the useful UI portion of #289 without carrying over its stale Strix workflow changes.

Verification

• git diff --check
• code-review-graph detect_changes risk score 0.00 for this slice
• Attempted: pnpm --dir frontend test -- src/app/calendar/page.test.tsx src/app/tasks/page.test.tsx (blocked locally because frontend/node_modules is not installed; CI will run in GitHub Actions)

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro

Run ID: be349bae-f45a-48e2-a06a-e923c318e4fa

📥 Commits

Reviewing files that changed from the base of the PR and between 02b9768 and 0fbb30a.

📒 Files selected for processing (5)

• AGENTS.md
• frontend/src/app/calendar/page.test.tsx
• frontend/src/app/tasks/page.test.tsx
• frontend/src/components/CalendarLayout.tsx
• frontend/src/components/TasksLayout.tsx

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/a11y-icon-button-labels-20260528

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[github-actions]

PR governance metadata gate is not ready for 0fbb30a34add665764484e032f715be8006cc24a:

• Current-head CodeRabbit issue comment has blocking warning/failure evidence on 0fbb30a.