docs: actionsFlexible covers both ways a row gives width back

It read as if a search field were the only way to earn it, which stopped being
true when the app and pipeline editors' rows started scrolling inside their own
box. Both are the same bargain — the box may shrink because its contents can —
and the flag is what the bar reads to allow it.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

frontend/src/lib/components/pageHeaderRegistry.svelte.ts

@@ -31,9 +31,11 @@ export type PageHeaderContent = {
 	/** Orders these buttons among the other registrations', ascending; registration order breaks a
 	 *  tie. For a menu that must stay at the far end however many pages register before it. */
 	actionsOrder?: number
-	/** These actions include something that can give width back — a search field rather than a row
-	 *  of buttons. On a phone the bar then lets their box shrink; without it the box holds its
-	 *  content width, because squeezing a row of buttons only pushes them out of the bar. */
+	/** These actions can give width back under pressure, so the bar lets their box shrink on a
+	 *  phone. Two ways to earn it: a control that is narrower when it has to be (the Runs filter
+	 *  row, whose search field yields), or a set that scrolls inside its own box (the app and
+	 *  pipeline editors, whose rows are too wide for any bar). Without it the box holds its content
+	 *  width, because squeezing a plain row of buttons only pushes them out of the bar. */
 	actionsFlexible?: boolean
 	/** Rendered right after the page's name in the breadcrumb: a mark that belongs to the name,
 	 *  like a documentation tooltip, or a control that acts on the thing named — an app's Edit,