fix(dashboard): position donut tooltips next to cursor and prevent edge clipping

[syndrome4002-leo]

Summary

• Donut tooltips on OSS Contributions and Issue Discoveries now anchor to the cursor: bottom-left at the cursor when the cursor is in the left half of the viewport, bottom-right when in the right half (so Ineligible donuts no longer push the tooltip past the right edge / sidebar).
• Tooltip is appended to document.body and positioned with viewport-aware edge handling (8 px margin), so it can't be clipped by MUI Card's overflow: hidden or by the main content area's scroll container on mobile/desktop.

Related Issues

Type of Change

• Bug fix
• New feature
• Refactor
• Documentation
• Other (describe below)

Screenshots

Before:

bandicam.2026-05-09.14-20-57-232.mp4

Now:

bandicam.2026-05-09.14-21-22-054.mp4

Before:

bandicam.2026-05-09.14-22-25-912.mp4

Now:

bandicam.2026-05-09.14-24-05-339.mp4

Checklist

• New components are modularized/separated where sensible
• Uses predefined theme (e.g. no hardcoded colors)
• Responsive/mobile checked
• Tested against the test API
• npm run format and npm run lint:fix have been run
• npm run build passes
• Screenshots included for any UI/visual changes