Add visual JSON datasource field picker

[Rello]

Adds a visual field picker beside the existing Object path input for local and external JSON datasources. Users can browse nested data, select fields, preview the extraction, and apply the existing path syntax while retaining manual editing.

Includes an authenticated JSON browsing endpoint, keyboard and mobile support, a sample JSON file, regression coverage, and consolidated unreleased changelog entries. New UI strings use the existing translation functions for extraction by Transifex.

Validation:

• PHPUnit: 232 tests, 746 assertions passed.
• JSON picker Playwright: local browsing and parser preview, array fields, cancellation, pagination, empty groups, mobile layout, invalid JSON, and external picker with a mocked response passed.
• REUSE lint and git diff --check passed.

Assisted-by: Codex:GPT-5

[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-10-18T08:52:04.241837Z	8194a4a	PR opened

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