feat: replace Radio page button descriptions with info-icon tooltips

[sg]

Summary

On Manage → Radio, the verbose descriptions next to the buttons are replaced with a compact info icon (a circled "i"). Hovering or focusing the icon shows the text; clicking pins it open (so it also works on touch).

Changes

• New web-ui/src/components/InfoTip.vue — circled-"i" icon; shows its text on hover/focus, click toggles pinned-open. Themed to match the UI and accessible (tabindex, role="button", aria-label, Enter/Space, blur-to-close).
• Manage.vue Radio tab — replaced the four descriptions with <InfoTip>:
  1. Advert (zero-hop vs flood)
  2. Flood-advert interval
  3. "Check contact table"
  4. Eviction policy / "Evict now" — this one was a paragraph below the buttons; moved into an info icon beside them so the page is uniform.
• Rebuilt webapi/static/ assets.

The only muted span left in the Radio tab is the (N free) data value, which is intentionally unchanged.

Testing

Front-end only (no API/schema changes). npm run build is clean. Tooltip is CSS hover/focus plus a click-to-pin toggle.