feat: UI/UX redesign for MCP Apps - 3 new apps + enhanced existing (#583)

Add workflow-list, execution-history, and health-dashboard apps.
Redesign operation-result with operation-aware headers, detail panels,
and copy-to-clipboard. Fix React hooks violations in validation-summary
and execution-history (useMemo after early returns). Add local preview
harness for development. Update tests for 5-app config.

Conceived by Romuald Członkowski - www.aiadvisors.pl/en

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

ui-apps/src/shared/styles/theme.css

@@ -1,21 +1,39 @@
 :root {
+  /* n8n brand colors */
   --n8n-primary: #ff6d5a;
   --n8n-primary-light: #ff8a7a;
+
+  /* Semantic colors */
   --n8n-success: #17bf79;
-  --n8n-success-light: #e8f9f0;
   --n8n-warning: #f59e0b;
-  --n8n-warning-light: #fef3cd;
   --n8n-error: #ef4444;
-  --n8n-error-light: #fee2e2;
   --n8n-info: #3b82f6;
-  --n8n-info-light: #dbeafe;
+
+  /* Dark mode defaults (fallback when host vars unavailable) */
   --n8n-bg: #1a1a2e;
   --n8n-bg-card: #252540;
   --n8n-text: #e0e0e0;
   --n8n-text-muted: #9ca3af;
   --n8n-border: #374151;
+  --n8n-error-light: #fee2e2;
+  --n8n-warning-light: #fef3cd;
+  --n8n-success-light: #e8f9f0;
+  --n8n-info-light: #dbeafe;
+
   --n8n-radius: 8px;
-  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
+  font-family: var(--font-sans, -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif);
+}
+
+[data-theme="light"] {
+  --n8n-bg: #ffffff;
+  --n8n-bg-card: #f9fafb;
+  --n8n-text: #1f2937;
+  --n8n-text-muted: #6b7280;
+  --n8n-border: #e5e7eb;
+  --n8n-error-light: #fef2f2;
+  --n8n-warning-light: #fffbeb;
+  --n8n-success-light: #f0fdf4;
+  --n8n-info-light: #eff6ff;
 }
 
 * {
@@ -25,8 +43,8 @@
 }
 
 body {
-  background: var(--n8n-bg);
-  color: var(--n8n-text);
+  background: var(--color-background-primary, var(--n8n-bg));
+  color: var(--color-text-primary, var(--n8n-text));
   line-height: 1.5;
   padding: 16px;
 }