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/styles/test/theme.test.ts

@@ -62,9 +62,9 @@ test("built-in themes use Plus Jakarta Sans and layered charcoal dark surfaces",
     '"Plus Jakarta Sans",ui-sans-serif,system-ui,sans-serif',
   );
   expect(t.themes.dark["font-sans"]).toBe('"Plus Jakarta Sans",ui-sans-serif,system-ui,sans-serif');
-  expect(t.themes.dark["color-bg"]).toBe("#101114");
-  expect(t.themes.dark["color-surface"]).toBe("#181a20");
-  expect(t.themes.dark["color-surface-2"]).toBe("#20232b");
+  expect(t.themes.dark["color-bg"]).toBe("#0c0d10");
+  expect(t.themes.dark["color-surface"]).toBe("#15171c");
+  expect(t.themes.dark["color-surface-2"]).toBe("#1c1f25");
 });
 
 test("resolveThemeName validates against configured names", () => {