Unify otel-ui on ds-* theme; restore redesigned Issues view

Restore IssuesVisualizer redesign reverted by merge 67ce419 and re-apply
Needle triage/test additions. Migrate all remaining screens off the MD3
palette, raw Tailwind colors, gradients and Material Symbols. Remove the
legacy theme block and fonts, drop the duplicate tab strip, rebuild
TelemetryFilters on FilterBar, and document status in AGENTS.md.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

otel-ui/index.html

@@ -7,10 +7,6 @@
     <title>HyperScope OTel — Distributed Telemetry</title>
     <link rel="preconnect" href="https://fonts.googleapis.com" />
     <link rel="preconnect" href="https://fonts.gstatic.com" crossorigin />
-    <link
-      href="https://fonts.googleapis.com/css2?family=Geist:wght@400;500;600;700&family=Inter:wght@400;500;600;700&family=JetBrains+Mono:wght@400;500;600;700&family=Material+Symbols+Outlined:opsz,wght,FILL,GRAD@20..48,100..700,0..1,-50..200&display=swap"
-      rel="stylesheet"
-    />
     <!-- Stackship design-spec typefaces: Bricolage Grotesque for headings and
          metric numbers, Instrument Sans for UI text, IBM Plex Mono for
          anything a person would copy or grep. -->
@@ -19,17 +15,15 @@
       rel="stylesheet"
     />
     <script>
-      // Applied synchronously, before first paint, so the redesigned screens
-      // (icon rail, top bar, filter bar, triage overview) don't flash the
-      // wrong theme. Screens still on the legacy palette ignore this
-      // attribute entirely - they have no light variant yet.
+      // Applied synchronously, before first paint, so no screen flashes the
+      // wrong theme.
       try {
         var storedTheme = localStorage.getItem("otel.ui.theme");
         if (storedTheme === "light") document.documentElement.dataset.theme = "light";
       } catch (e) {}
     </script>
   </head>
-  <body class="bg-background text-on-surface min-h-screen antialiased">
+  <body class="bg-ds-bg text-ds-text min-h-screen antialiased">
     <div id="root"></div>
     <script src="/static/otel-rum.js"></script>
     <script type="module" src="/src/main.tsx"></script>