Add sort plugin for managing orderable entities

[dswbx]

This PR introduces a new plugin that enables automatic position management for sortable entities with support for scoped sorting.

Features:

• Automatic position assignment on insert (starting from 0)
• Automatic reordering when positions are updated
• Scoped sorting (e.g., sort within categories or projects)
• API endpoints for manual reordering and recalculation
• Batch recalculation support for large datasets

Usage:

import { sort } from "bknd/plugins";

const app = createApp({
  plugins: [
    sort({
      entities: {
        tasks: {
          field: "position",
          scope: "project_id", // optional
        },
      },
    }),
  ],
});

The plugin automatically adds the sort field to configured entities and creates two API endpoints per entity:

• POST /api/sort/{entity}/reorder - move an item to a new position
• POST /api/sort/{entity}/recalculate - recalculate all positions (useful for cleanup)

When a scope field is specified, sorting only happens within items that share the same scope value.

[cameronapak]

Where do you feel the status of this PR is?

[dswbx]

in my shallow tests it worked good, but it would need more testing :)