## What kind of change does this PR introduce?
Chore that references DEPR-394.
## What is the current behavior?
Key/value editors for headers are implemented separately in multiple
places.
## What is the new behavior?
DEPR-394 is consolidating repeated RHF field-array UIs across Studio and
the design system.
- adds a shared `KeyValueFieldArray` component in `ui-patterns`
- adds a shared `httpHeaderAddActions` helper for preset header rows
- migrates the key/value header editors in:
- Platform Webhooks
- Cron Jobs HTTP headers
- Database Webhooks HTTP headers
- documents the key/value pattern in the design system with:
- a dedicated fragment page
- updated forms guidance
- updated form pattern demos
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| <img width="1102" height="420" alt="CleanShot 2026-03-23 at 12 22
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src="https://github.com/user-attachments/assets/f8d23ff9-7063-462f-8074-b400561f77e9"
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## Additional context
This is PR 1 of a 3-PR stack for DEPR-394.
Danny White