Fix language bar hover tooltip

[eutv2022]

Summary

• Replace the language bars' destructive logout click handler with a non-destructive hover/focus target.
• Add a visible tooltip showing the language name and percentage on hover and keyboard focus.
• Preserve the existing language color bars and native accessibility label.

Verification

• npm run typecheck:web
• npx eslint src/renderer/src/components/GitHubStatsWidget.tsx (0 errors; existing unused eslint-disable warning only)
• npm run build
• git diff --check

Close #8