feat: dashboard theme overhaul — light content area with branded teal sidebar

Complete frontend visual redesign using certctl logo color palette:
- Deep teal sidebar (#0c2e25) with prominent centered logo (64px in white pill)
- Light content area (#f0f4f8) with white cards and visible borders
- Brand colors from logo: teal (#2ea88f), blue (#3b7dd8), orange (#e8873a), green (#4ebe6e)
- Inter + JetBrains Mono typography, colored stat card top borders
- All 17 pages + 7 components updated (25 files, ~700 lines changed)
- 15 new dashboard screenshots replacing old dark theme screenshots
- Prometheus metrics e2e test added, integration test mock fixes
- Docs updated: architecture.md theme description, testing-guide.md DNS-PERSIST-01 coverage

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

web/src/components/ErrorState.tsx

@@ -5,12 +5,12 @@ interface ErrorStateProps {
 
 export default function ErrorState({ error, onRetry }: ErrorStateProps) {
   return (
-    <div className="flex flex-col items-center justify-center py-16 text-slate-400">
-      <svg className="w-12 h-12 text-red-400 mb-4" fill="none" viewBox="0 0 24 24" stroke="currentColor" strokeWidth={1.5}>
+    <div className="flex flex-col items-center justify-center py-16 text-ink-muted">
+      <svg className="w-12 h-12 text-red-700 mb-4" fill="none" viewBox="0 0 24 24" stroke="currentColor" strokeWidth={1.5}>
         <path strokeLinecap="round" strokeLinejoin="round" d="M12 9v3.75m-9.303 3.376c-.866 1.5.217 3.374 1.948 3.374h14.71c1.73 0 2.813-1.874 1.948-3.374L13.949 3.378c-.866-1.5-3.032-1.5-3.898 0L2.697 16.126zM12 15.75h.007v.008H12v-.008z" />
       </svg>
-      <p className="text-sm mb-2">Failed to load data</p>
-      <p className="text-xs text-slate-500 mb-4">{error.message}</p>
+      <p className="text-sm mb-2 text-ink">Failed to load data</p>
+      <p className="text-xs text-ink-faint mb-4">{error.message}</p>
       {onRetry && (
         <button onClick={onRetry} className="btn btn-primary text-xs">
           Retry