feat(category): cascade-select category tree via folder icon - #707

Adds folder-icon cascade selection for category trees, backed by a bounded descendant endpoint.

Changes:

• Adds descendant retrieval with a 5,000-node limit.
• Updates tree cascade selection and unsaved-change tracking.
• Adds localized messages and changelog documentation.

Suppressed comments (3)

packages/Webkul/Admin/src/Resources/views/components/tree/item.blade.php:560

• The cascade mutates children and immediately emits change-input, but the newly fetched descendant components do not mount (and therefore do not register their labels) until Vue's next render. v-product-categories.onTreeSelection() snapshots this.$refs.tree.labels during this event, so the newly selected codes are missing from labelByCode and the category summary falls back to a count until another selection event occurs. Wait for the render tick before emitting, or register the fetched labels directly.
  packages/Webkul/Admin/src/Resources/views/components/tree/item.blade.php:617
• The recursive sync also visits leaf nodes. For a mounted leaf, children is empty, so setting hasFetchedChildren and showChildren here gives it a chevron and an empty expandable branch after a parent cascade. Only synchronize mounted descendants when children.length is non-zero.
  packages/Webkul/Admin/src/Resources/views/components/tree/item.blade.php:571
• This request sends only the category id, while the initial product category tree explicitly requests the active channel locale (categories.blade.php:268). CategoryTreeResource resolves labels from the request locale and otherwise uses the global requested locale, so when the editor falls back to a channel's first locale the newly fetched subtree can switch languages. Pass the active locale through this component and validate/use it in the descendants request.

• Files reviewed: 41/41 changed files
• Comments generated: 5
• Review effort level: Lite