Docs: restructure Extend section with API, Webhooks, and Apps pages (#18517)

## Summary
- Restructures the developer Extend documentation: moves API and
Webhooks to top-level pages, creates dedicated Apps section with Getting
Started, Building, and Publishing pages
- Updates navigation structure (`docs.json`, `base-structure.json`,
`navigation.template.json`)
- Updates translated docs for all locales and LLMS.md references across
app packages

## Test plan
- [ ] Run `mintlify dev` locally and verify navigation structure
- [ ] Check that all links in the Extend section work correctly
- [ ] Verify translated pages render properly


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Co-authored-by: github-actions <github-actions@twenty.com>

packages/twenty-docs/user-guide/getting-started/capabilities/what-is-twenty.mdx

@@ -36,7 +36,7 @@ Open-source is the bedrock of our approach, ensuring that Twenty evolves with it
 - **Dashboards:** Track performance with custom reports and visualizations. [View dashboards](/user-guide/dashboards/overview).
 - **Permissions & Access:** Control who can view, edit, and manage your data with role-based permissions. [Configure access](/user-guide/permissions-access/overview).
 - **Notes & Tasks:** Create notes and tasks linked to your records for better collaboration.
-- **API & Webhooks:** Connect to other apps and build custom integrations. [Start integrating](/developers/extend/capabilities/apis).
+- **API & Webhooks:** Connect to other apps and build custom integrations. [Start integrating](/developers/extend/api).
 
 
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