## Scope & Context
Closes#20358.
The Apps docs were restructured into nested pages, but the generated
docs navigation source still pointed to the old flat Apps page slugs.
This made Developers > Apps navigation entries point to removed English
docs pages.
## Technical inputs
- Update `packages/twenty-docs/navigation/base-structure.json` to use
the current nested Apps docs structure.
- Regenerate `packages/twenty-docs/docs.json` and
`packages/twenty-docs/navigation/navigation.template.json` from the
updated structure.
- Update `generate-docs-json.ts` so localized navigation falls back to
the English slug when the localized `.mdx` file does not exist yet,
avoiding generated 404 links while translations catch up.
## Validation
- Parsed `docs.json`, `base-structure.json`, and
`navigation.template.json` as valid JSON.
- Checked all generated navigation page slugs against existing `.mdx`
files: `missing nav mdx 0`.
- Checked Apps navigation specifically: `missing apps nav mdx 0`.
`yarn docs:generate` could not be run in this local environment because
Yarn/Corepack is not installed here, so I regenerated the JSON files
with the same generator logic via Node.
Co-authored-by: dev111-actor <dev111-actor@users.noreply.github.com>
