feat(frontend): show raw counts in overview metric popovers

[Nissivardhan]

Updates overview metric cards to expose raw counts while keeping percentages visible.

Purpose

Percentages are visible in the overview cards, but the corresponding raw counts are not easily discoverable. This change keeps percentages visible while exposing counts through an
interaction that works for mouse, keyboard, and touch users.

Implementation

• Extend the overview rate card data model with optional count
• Map delivered, opened, clicked, and bounced counts into the overview and task analytics card data
• Wrap metric cards with a popover when count data exists
• Show the count label in the popover on hover, focus, and click/tap
• Add i18n strings for count labels in English, Chinese, and Japanese

Testing

• Frontend build passed with pnpm build
• Verified locally in the overview dashboard and task analytics page
• Confirmed percentages remain visible and counts appear via popover interaction

Additional Context

Short screen recording attached below.
Screencast from 2026-03-22 13-28-47.webm