exp(06): focused investigation — visual hierarchy without layout changes

Emphasise the active investigation card through stronger elevation,
clearer borders, and improved spacing. Quiet supporting panels by
reducing border opacity, softening heading weight, and lowering
text contrast — making them available without competing for attention.

Facilitator card receives a warm surface tint to read as a briefing
card rather than a generic panel.

Documentation: close experiment 05 with findings, add experiment 06
to the design evolution log, add Attention Hierarchy to UX guidelines,
defer dark mode to a future Investigation Mode experiment.

Presentation changes only — no reasoning, prompts, graph, API, or
backend modifications.

components/investigation-map.jsx

@@ -82,15 +82,15 @@ export default function InvestigationMap({ turnCount = 0 }) {
   if (!hasActiveTopics && groups.established.length === 0) return null;
 
   return (
-    <div className="rounded-lg border border-gray-100 bg-gray-50/50 p-4" role="region" aria-label="Investigation map preview">
-      <h2 className="mb-1 text-sm font-semibold tracking-tight text-gray-400">
+    <div className="rounded-lg border border-gray-200/60 bg-gray-50/30 p-4" role="region" aria-label="Investigation map preview">
+      <h2 className="mb-1 text-[11px] font-medium tracking-widest uppercase text-gray-300">
         Investigation Map
       </h2>
-      <p className="mb-3 text-xs text-gray-400">
+      <p className="mb-3 text-xs text-gray-400/70">
         Active investigation topics and their status.
       </p>
 
-      <div className="space-y-px border-t border-gray-100 pt-3" role="list" aria-label="Investigation topics">
+      <div className="space-y-px border-t border-gray-200/60 pt-3" role="list" aria-label="Investigation topics">
         {topics.map((topic, i) => (
           <TopicRow key={`${topic.title}-${i}`} title={topic.title} status={topic.status} />
         ))}