fix(learn,ui): the open assistant field holds still: no flicker, no sliding away, no resizing under the keyboard (ADR 0021, D69)

Inside a studyset the field flickered as it opened and closed: the
floating location switched between a raised centre and the centre,
which Scaffold animates by scaling the button out and in. It keeps one
location now, raised above the licence line by padding. While open it
no longer slides away as the studyset or the Library scrolls
(ScrollHidingFab.pinned, new), and the keyboard covers Home, the
Library, a studyset and a session rather than shrinking them; the field
lifts itself by as much of the keyboard as reaches above it.
NavigationFrame no longer resizes for the keyboard itself, leaving it
to each tab's own scaffold, which still does by default (Todo's,
Train's and Meditate's tests pass unchanged).

Whats-New: Inside a studyset, the question field opens without flickering, stays while you scroll, and the screen no longer jumps when the keyboard comes.
Whats-New-De: In einem Lernset öffnet sich das Fragefeld ohne Flackern, bleibt beim Scrollen stehen, und der Bildschirm springt nicht mehr, wenn die Tastatur kommt.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

packages/halkyon_ui/lib/src/widget/navigation_frame.dart

@@ -152,6 +152,11 @@ class _NavigationFrameState() extends State<NavigationFrame> {
             // it, as iOS 26's tab bar floats over content; their lists end
             // with room for it (the body's bottom padding says how much).
             extendBody: !widget.hidesNavigationBar,
+            // The keyboard is each screen's own to make way for, its own
+            // scaffold resizing as it does by default: a screen with a field
+            // floating over it keeps its size and lifts the field instead
+            // (Halkyon Learn's ADR 0021, D69).
+            resizeToAvoidBottomInset: false,
             body: widget.child,
             // Without the bar, a strip as high as the system's own bar, in
             // the screen's background, keeps every screen inside clear of