feat(core): re-bucket pinned docks into a dedicated ~pinned category

[antfubot]

Description

Reworks the dock pin feature. Previously, pinning a dock only floated it to the top of its existing category bucket — it could never jump ahead of higher-priority categories. Now pinning re-buckets the entry into a dedicated ~pinned category with a strongly-negative order weight (-100000), so pinned entries lead the dock bar ahead of every real category.

The re-bucketing respects the dual role of category:

• A top-level entry (or a whole group button) pins into the bar-level ~pinned bucket.
• A grouped member pins into a ~pinned sub-category that leads its own group, staying folded inside the group rather than surfacing on the top-level bar.

~pinned is chosen before the category-hide check and is itself never hideable, so a pinned entry stays visible even when its home category is hidden. Unpinning returns the entry to its home category in its previous position.

The whole feature stays client-side: the ~pinned order is a local override in the sort rather than an edit to the upstream DEFAULT_CATEGORIES_ORDER table (the docksPinned shared-state field is unchanged, so no migration). The old "pinned-first" intra-category tiebreaker is removed since pin now changes the bucket. Docs are updated, including a fix to the defaultOrder description (the code sorts ascending — lower first — not "higher first" as previously documented).

Linked Issues

Additional context

New tests in dock-groups.test.ts cover top-level pin → ~pinned, group-button pin → top-level ~pinned, grouped-member pin → ~pinned sub-category (no bar promotion), the -100000 lead ordering, pin overriding category-hide, and the intra-~pinned sort. pnpm lint && pnpm test && pnpm typecheck && pnpm build all pass.

This PR was created with the help of an agent.