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/csr/test/reactive.test.ts

@@ -37,6 +37,14 @@ function mount(html: string, runtime = REACTIVE_RUNTIME, controllers = ""): Wind
 
 const REPLACED_GLOBALS = ["window", "document", "location", "fetch", "MutationObserver"];
 
+test("optional properties and nullish fallbacks hydrate without crashing", () => {
+  const win = mount(`<div data-scope="records: null, row: { count: 0 }, items: ['ok']"><b data-text="records?.rows?.length ?? 0"></b><i data-text="row?.count ?? 5"></i><em data-text="items?.[0] ?? 'empty'"></em><u data-text="!records?.rows?.length"></u></div>`);
+  expect(win.document.querySelector("b")?.textContent).toBe("0");
+  expect(win.document.querySelector("i")?.textContent).toBe("0");
+  expect(win.document.querySelector("em")?.textContent).toBe("ok");
+  expect(win.document.querySelector("u")?.textContent).toBe("true");
+});
+
 restoreGlobalsAfterAll(REPLACED_GLOBALS);
 
 beforeEach(() => {