fix(website): scope subcategory filter values to parent category

Subcategories with the same name (e.g. 'Frameworks') across different
top-level categories were sharing a filter value, so clicking one
subcategory tag would match entries from unrelated categories.

Each subcategory now stores both a display name and a scoped value
('Category > Subcategory') used for data-cats matching. The template
renders the display name on tags and mobile-cat span, but uses the
scoped value for filtering. Subcategory tags are also moved before
category tags so the most-specific label appears first.

Co-Authored-By: Claude <[email protected]>