Disable named view transition on admin page-content wrapper

The <ViewTransition name="page-content"> wrapper around the admin
main content was triggering a 'shared element' morph on every page
load and navigation: the browser tries to animate the bounding box
of the named element across the old and new pages, and since each
admin page has a different height, the browser was scaling the
snapshot from the top-left corner. That read as the page 'loading
from the corner with keyframes' and pushed the bottom of the
content to the top during the transition.

Setting update="none" opts out of the named transition entirely.
The children just swap on navigation — no fade, no scale, no morph.
The AdminSidebar + parchment background stay mounted across
navigations so the cut reads as a content swap inside a stable
shell, which is what the eye expects for a logged-in admin app.

The ::view-transition-old(page-content) / ::view-transition-new
CSS rules in globals.css are left in place in case we want to
re-enable with a different shape later (pure-opacity rules on the
root pseudo-elements instead of a named wrapper).

src/components/transitions/SmoothViewTransition.tsx

@@ -4,48 +4,29 @@ import { ViewTransition } from "react";
 import type { ReactNode } from "react";
 
 /**
- * Smooth view-transition wrapper for any page-section content.
+ * Page-content wrapper. The named `page-content` view transition used
+ * to apply a CSS-driven crossfade (::view-transition-old/new rules in
+ * globals.css) on every navigation. The opacity fade itself was fine,
+ * but because the named transition attaches `view-transition-name:
+ * page-content` to the wrapper, the browser also tries to morph the
+ * wrapper's bounding box across pages — and since each admin page has
+ * a different height, the browser was scaling the snapshot from the
+ * top-left corner, which read as the page "loading from the corner"
+ * and pushed the bottom of the content to the top during the
+ * transition.
  *
- * Drop this around the main content area of a route (or around an
- * individual <Suspense> chunk) to opt that subtree into a soft
- * crossfade on navigation. The browser's native View Transitions API
- * handles the actual animation — when the browser doesn't support it,
- * the children just swap, no error.
+ * `update="none"` opts out of the named transition entirely. The
+ * children just swap on navigation (no fade, no scale, no morph) —
+ * the AdminSidebar + parchment background stay mounted across
+ * navigations so the cut reads as a content swap inside a stable
+ * shell, which is what the eye expects for a logged-in admin app.
  *
- * `name` groups elements so the browser can morph the same element
- * across pages. Use the same name on the source and destination (e.g.
- * the page header) for shared-element morphing. Use the default
- * `"page-content"` for plain crossfades.
- *
- * Motion note: the CSS-side ::view-transition-old/new rules are a
- * 90/140ms pure-opacity fade with NO translate. Earlier versions
- * shifted the page 4-6px on enter/exit which compounded with the route
- * content settling into place and read as a small "drop" — bad for
- * vestibular comfort. A flat opacity crossfade softens the cut
- * without any positional movement.
- *
- * Usage:
- *   <main>
- *     <SmoothViewTransition>{children}</SmoothViewTransition>
- *   </main>
+ * If we ever want a subtle crossfade back, the right shape is a
+ * pure-opacity ::view-transition-old/new pair with NO named wrapper
+ * (i.e. drop the `name` prop and add the rules to
+ * ::view-transition-old(root) / ::view-transition-new(root) so the
+ * browser doesn't morph the bounding box).
  */
-export function SmoothViewTransition({
-  children,
-  name = "page-content",
-}: {
-  children: ReactNode;
-  name?: string;
-}) {
-  return (
-    <ViewTransition
-      name={name}
-      // `default` runs a CSS-driven crossfade using the
-      // ::view-transition-* pseudo-elements defined in globals.css.
-      // Other options: "none" (instant cut), or a custom string your
-      // CSS can match.
-      update="default"
-    >
-      {children}
-    </ViewTransition>
-  );
+export function SmoothViewTransition({ children }: { children: ReactNode }) {
+  return <ViewTransition update="none">{children}</ViewTransition>;
 }