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/src/reactive-runtime.ts

@@ -5542,7 +5542,11 @@ export const REACTIVE_RUNTIME = String.raw`
     function parsePostfix() {
       var node = parsePrimary();
       for (;;) {
-        if (match(".")) {
+        var optional = match("?.");
+        if (optional && !is("[") && !is("(")) {
+          var optionalProp = next().value;
+          node = { value: node.value == null ? undefined : node.value[optionalProp], obj: node.value };
+        } else if (match(".")) {
           var prop = next().value;
           node = { value: node.value == null ? undefined : node.value[prop], obj: node.value };
         } else if (match("[")) {
@@ -5617,6 +5621,10 @@ export const REACTIVE_RUNTIME = String.raw`
     }
     function parseTernary() {
       var c = parseOr();
+      while (match("??")) {
+        var fallback = parseOr();
+        c = c == null ? fallback : c;
+      }
       if (match("?")) { var a = parseTernary(); expect(":"); var b = parseTernary(); return c ? a : b; }
       return c;
     }
@@ -5782,6 +5790,12 @@ export const REACTIVE_RUNTIME = String.raw`
 
       var two = input.slice(i, i + 2);
 
+      if (two === "?." || two === "??") {
+        tokens.push({ type: "operator", value: two });
+        i += 2;
+        continue;
+      }
+
       if (
         two === "==" ||
         two === "!=" ||