Add paging to the icon picker

[kmcginnes]

Description

The icon picker (added in #1777) capped the grid at 64 icons and told users to "type to search" — there was no way to browse the rest of the Lucide library. This adds paging so every icon is reachable.

• Paging — the grid now pages through the full filtered/unfiltered list, 64 icons per page, with a minimal footer (Page X of Y + prev/next chevrons) modeled on the query results list footer. filterIcons returns the full match list instead of stopping at a hard cap.
• Page persistence — page position is component-local state, so the picker reopens on the same page while the Node Style dialog stays open; it resets on search and when the dialog reopens (the picker unmounts).
• Tooltips — each icon now uses the Button tooltip prop instead of the native title, giving a styled tooltip and an aria-label accessible name.

Suggested reading order: IconPicker.tsx (component + new PagerFooter), then IconPicker.test.tsx.

Validation

• pnpm checks passes (lint, format, types)
• pnpm test passes (1787 tests; IconPicker.tsx at 100% line coverage)
• Manual: open the Node Styling panel for a vertex type, click Browse, page through with the chevrons, type to filter (resets to page 1), select an icon on a later page and reopen to confirm it returns to that page.

The vitest.config.ts change is the repo's automatic coverage-threshold ratchet, not a hand edit.

Related Issues

• Related to Add built-in Lucide icon library for node styling #1777

Check List

• I confirm that my contribution is made under the terms of the Apache 2.0 license.
• I have verified pnpm checks passes with no errors.
• I have verified pnpm test passes with no failures.
• I have covered new added functionality with unit tests if necessary.
• I have updated documentation if necessary.