refactor!: Replace SortableJS 4/4: remove the SortableJS dependency entirely

[6pac-ai]

Context

Final part of the SortableJS removal (port of slickgrid-universal's refactor(core)!: drop SortableJS dependency #2634). Stacked on the DraggableGrouping port PR. Column reordering and draggable grouping now run entirely on the built-in native HTML5 drag & drop engines in slick.interactions.js, so SlickGrid ships with zero runtime dependencies.

What's in here

• package.json — the dependencies block is gone (sortablejs was its only entry); package-lock.json regenerated. A transitive sortablejs entry remains in the lock only through vite-demo's dependency on the published slickgrid@5.x package and disappears automatically on the next release.
• Examples/tests sweep — the two SortableJS <script> tags (jsdelivr CDN + local fallback) removed from 103 example/test pages (149 lines, pure deletions); examples/sortable-cdn-fallback.js deleted. Nothing needed adding anywhere: every page already loads slick.interactions.js, which now carries the drag engines.
• src/global.d.ts — the Sortable global declaration and its type import are gone.
• eslint.config.mjs — Sortable removed from globals.
• vite-demo — sortablejs dependency and the window.Sortable = Sortable shim removed.
• scripts/builds.mjs — stale SortableJS-related comment removed.
• README.md — the "1 small dependency" note becomes a zero-runtime-dependencies note; the historical v3 jQueryUI→SortableJS references are left as history.
• The .slick-sortable-placeholder and .slick-droppable-sortitem-hover CSS class names are intentionally kept so consumers' custom CSS keeps working.

BREAKING CHANGE

SortableJS is no longer used nor required:

• Consumers loading SlickGrid via script tags can delete their SortableJS <script> include; the window.Sortable global is no longer read.
• Column reordering requires slick.interactions.js to be loaded (it already was in every example and is imported by the esm/cjs bundles).
• SlickDraggableGrouping.getSetupColumnReorder() returns { columnReorderDragInstance } (changed in the previous part of this series).

A short wiki migration note (mirroring the v3/v4 removal pages) would be worth adding at release time.

Verification

• Full 47-spec Cypress suite: 600/601 passing, 0 failures (1 intentional pending) with SortableJS absent from the dependency tree, every example page, and the globals.
• Lint and strict TS declaration build clean.
• Grepping the repo for sortablejs leaves only historical comments and the intentionally-kept CSS class names; the swept pages were spot-checked over HTTP to confirm they serve with zero references.

🤖 Generated with Claude Code