feat(extension): add beta badge to Agents tab

[iscekic]

Summary

• Adds a small brand-tinted BETA pill next to the Agents tab in the side panel mode switch.
• Reuses the existing session status badge vocabulary (rounded-full, tinted background) and existing design tokens only.
• Pill is aria-hidden; the tab accessible name is now Agents beta so screen readers announce it once.

Verification

• pnpm --filter kilo-extension verify (typecheck, lint, 1395 unit tests) passed.
• pnpm --filter kilo-extension build passed.
• E2E skipped: change is one isolated component; existing specs match getByRole('tab', { name: 'Agents' }) by substring, so they stay green.

[kilo-code-bot]

Code Review Summary

Status: No Issues Found | Recommendation: Merge

Executive Summary

Reviewed the Agents tab beta badge change in agents-mode-switch.tsx; the aria-hidden pill plus Agents beta accessible name is correct and existing Playwright substring locators remain valid.

Files Reviewed (1 files)

• apps/extension/entrypoints/sidepanel/agents-mode-switch.tsx

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_{Reviewed by grok-4.6 · Input: 84K · Output: 4.5K · Cached: 150.5K}

_{Review guidance: REVIEW.md from base branch main}