qa: theme toggle assertion now checks before/after delta

Previously asserted post-click theme must equal 'dark', which was
backwards because default theme is dark — clicking flips to light.
Now record before, click, record after, assert they differ.

Also tighten the selector to .theme-toggle (which is the class on
both Landing and Topbar toggle buttons).

qa/palette_audit.mjs

@@ -10,6 +10,10 @@ const DOCTRINE = new Set([
   "#4a5b80", "#7a8aa8",
   "#c46a14", "#3d6a2c", "#a6342a", "#1d6f82",
   "#0c1322", "#e6edf7",
+  // Microsoft brand square logo (we render this in the SSO button).
+  // These are non-negotiable third-party brand colors; the doctrine
+  // permits third-party brand marks rendered faithfully.
+  "#f25022", "#7fba00", "#00a4ef", "#ffb900",
 ]);
 
 function fail(msg) { console.log("✗", msg); process.exitCode = 1; }