bugfix: reader-nav is fully fixed; no settle-on-scroll (0.21.3)

frontend/src/lib/styles/tokens.css

@@ -61,10 +61,12 @@
     --icon-lg: 22px;
 
     /* App-frame heights (fixed-position bars at the top and bottom of
-       the viewport). Used by the layout + reader to reserve content
-       space and animate fullscreen mode. Recomputed once if the
-       header padding/font-size ever changes — keep in sync. */
+       the viewport). These are first-paint fallbacks — the real
+       values are written by ResizeObservers on the actual elements
+       in +layout.svelte and the reader, so they reflect rendered
+       size and survive font / zoom / wrap changes. */
     --app-header-h: 60px;
+    --reader-nav-h: 56px;
     --reader-bar-h: 56px;
 
     --z-dropdown: 10;