feat(header): add opt-in auto-hide-on-scroll for the header (#6738)

* feat(header): add opt-in auto-hide-on-scroll for the header

New per-user header preference (default off): when enabled, the
header slides away while scrolling down and reappears on scroll-up or
near the top of the page. Disabled while in board edit mode, and
skipped entirely while focus is inside the header. Only applies when
the header is set to visible - the existing hover-to-reveal floating
controls already cover the hidden-header case.

* chore(api): regenerate the checked-in OpenAPI schema

check:openapi was failing in CI - the schema on disk hadn't been
regenerated after the header preferences gained autoHideOnScroll.

Add scripts/generate-openapi-schema.mts (and a generate:openapi
package script) alongside the existing check script so this is a
one-command fix next time the schema drifts.

* docs(users): document the header studio's visibility and auto-hide options

Header customization (drag-to-arrange controls, hide/show, hover-reveal
and pin, auto-hide-on-scroll) had no documentation on the user general
settings page.

apps/docs/docs/management/users/index.mdx

@@ -77,6 +77,17 @@ Choose the first day of the week for the user. This will affect the calendar wid
 
 Option to show icons for status check instead of colored dots.
 
+#### Header studio
+
+Personal control over what appears in the header and where. Drag controls between the Left, Center, and Right
+sections, add optional board shortcuts, and choose how the search and logo controls are displayed.
+
+The header can be hidden entirely with the visibility toggle. While hidden, hovering the top edge of the page
+reveals it temporarily; clicking inside it pins it open until the page is refreshed or you click elsewhere.
+
+When the header is visible, the **Auto-hide on scroll** toggle makes it slide away while scrolling down and
+reappear on scroll-up or near the top of the page. It has no effect while the header itself is hidden.
+
 #### Delete
 
 This action will permanently delete the user from the database, including any preferences they set.