docs: add code examples to migrating_api article

[noliveleger]

Summary

• Added an Authentication section explaining the Authorization: Token xxxx header with curl, Python (requests), and R (httr) examples
• Added code examples (curl / Python / R) to every endpoint section: project list, submission data, form details, tags, permissions, metadata, and user profile
• Restructured each section with #### Code examples before #### Response examples for faster scanning
• Wrapped response examples in <details> blocks to reduce visual noise
• Fixed a Markdown rendering bug in the Form endpoints field mapping table (missing blank line before table)
• Updated Last updated date to 19 May 2026 (commit ID still need to be changed)
• Applied all changes to the French, Spanish, and Arabic locales

[jnm]

The stated purpose of this article is explaining "how to migrate your API integrations", but we lack any way to educate the readership (which is large because we published an in-app message linking here) as to whether this information applies to them at all.

Perhaps we should include a section to help people, even extremely non-technical people who will have clicked an important-looking link and ended up here, understand if they will actually be affected in any way.

We should further guide people to our articles about using synchronous exports to connect to common platforms, such as:

• https://support.kobotoolbox.org/pulling_data_into_excelquery.html
• https://support.kobotoolbox.org/pulling_data_into_powerbi.html

Integrations using synchronous exports will NOT need any modification; they are totally fine as-is!