Fix empty and duplicated glossary breadcrumb items

## Why this needs addressing

The live JSON-LD on `https://forrt.org/glossary/english/h_index/` currently contains:

- position 2, `name: "Glossary"`, with an empty `item`;
- position 3, another `name: "Glossary"`, pointing to `/glossary/english/`.

This comes from `layouts/partials/structured-data/breadcrumbs.html` walking the stub `/glossary/` ancestor and the language section independently.

## Requested change

After the glossary hub is repaired, make the breadcrumb trail explicit for glossary pages:

- FORRT → Glossary (the real hub URL) → English/German/Chinese/Arabic/Turkish → term;
- every `ListItem` has a non-empty, canonical `item` URL;
- labels are unique and describe their level;
- positions are sequential and the final item is the current page.

Apply equivalent validation to curated resources and other deep sections.

## Acceptance criteria

- No generated breadcrumb contains an empty item or duplicated level label.
- Representative glossary pages pass JSON parsing and the Rich Results Test.
- The fix does not create multiple competing BreadcrumbList blocks.

Reference: https://developers.google.com/search/docs/appearance/structured-data/breadcrumb