chore(release): redesign UI tokens and publish styles 0.8.26, ui 0.8.86

Visual-only redesign ("instrument panel"): cool graphite neutrals for light
and dark, layered hairline elevation, larger radii, a mono token for
eyebrows/data, keycap-style solid and secondary buttons, recessed input
wells and tab tracks, a stronger dialog, and a theme-driven focus outline.
No props, outputs or behaviour change.

Also records the already-published csr 0.8.42, styles 0.8.25 and ui 0.8.85
changes (optional chaining/nullish in the reactive runtime, shared
theme/accent cookie sync, BackToTop hidden attribute).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

packages/ui/components/BackToTop.wrn

@@ -36,6 +36,7 @@ component BackToTop {
       data-show-label='{showLabel ? "true" : "false"}'
       data-progress='{showProgress ? "true" : "false"}'
       data-show='{alwaysVisible || visible}'
+      hidden='{!alwaysVisible && !visible}'
       class='wrn-back-to-top {class}'
       style='--wrn-back-to-top-progress: {progress}%;'
       @window:scroll='visible = window.scrollY >= threshold; progress = Math.min(100, Math.max(0, Math.round((window.scrollY / Math.max(1, document.documentElement.scrollHeight - window.innerHeight)) * 100)))'
@@ -58,6 +59,10 @@ component BackToTop {
   }
 
   style {
+    .wrn-back-to-top[hidden] {
+      display: none;
+    }
+
     .wrn-back-to-top {
       --back-accent: var(--wrn-color-primary);
       --back-accent-hover: var(--wrn-color-primary-hover);