feat(reviewiq): Add AI synthesis support to dashboard components

Frontend:
- Add Synthesis type with action plan, insights, annotations
- ExecutiveSummary: Accept synthesis prop for AI narrative
- SentimentPie: Accept insight prop for contextual explanation
- IntensityHeatmap: Accept insight + highlightDomain props
- TimelineChart: Accept insight + annotations props
- All components gracefully degrade when synthesis is null

Backend:
- Add Stage 4: Synthesize for generating AI narratives
- Gathers context from classified spans
- Generates executive narrative, section insights, action plan
- Produces timeline annotations and marketing angles
- Stores synthesis in pipeline.executions table

Components show AI insights with purple gradient styling when available,
fall back to existing behavior when synthesis is not yet generated.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

web/components/reviewiq/insights/ExecutiveSummary.tsx

@@ -16,7 +16,7 @@ import {
   Award,
 } from 'lucide-react';
 import { useTranslation } from '@/hooks/useTranslation';
-import type { Insights, WeaknessItem, OpportunitySpan, OpportunityMatrix, DomainScore, URTDomain } from '../types';
+import type { Insights, WeaknessItem, OpportunitySpan, OpportunityMatrix, DomainScore, URTDomain, Synthesis } from '../types';
 import { getSubcodeDefinition } from '@/lib/taxonomy/data';
 
 interface ExecutiveSummaryProps {
@@ -25,6 +25,8 @@ interface ExecutiveSummaryProps {
   domainScores?: DomainScore[];
   onDriverClick?: (subcode: string) => void;
   onDomainClick?: (domain: URTDomain) => void;
+  // AI-generated narrative (optional - enhances when available)
+  synthesis?: Synthesis | null;
 }
 
 // User-friendly domain config
@@ -199,10 +201,14 @@ export function ExecutiveSummary({
   domainScores,
   onDriverClick,
   onDomainClick,
+  synthesis,
 }: ExecutiveSummaryProps) {
   const { strengths, weaknesses, executive_summary, opportunity_matrix, rating_simulator } = insights;
   const [showFullSummary, setShowFullSummary] = useState(false);
 
+  // Use AI narrative if available, otherwise fall back to generated summary
+  const narrativeText = synthesis?.executive_narrative || executive_summary;
+
   const topStrength = strengths[0];
   const topWeakness = weaknesses[0];
   const ratingDisplay = getRatingDisplay(avgRating);
@@ -286,16 +292,23 @@ export function ExecutiveSummary({
       </div>
 
       {/* AI Summary */}
-      {executive_summary && (
+      {narrativeText && (
         <div className="px-6 pb-4">
-          <div className="p-4 bg-white/70 rounded-xl border border-blue-100">
+          <div className={`p-4 rounded-xl border ${
+            synthesis?.executive_narrative
+              ? 'bg-gradient-to-r from-purple-50 to-blue-50 border-purple-200'
+              : 'bg-white/70 border-blue-100'
+          }`}>
             <div className="flex items-start gap-2">
-              <span className="text-lg">💡</span>
-              <div>
-                <p className={`text-gray-700 leading-relaxed ${!showFullSummary && 'line-clamp-2'}`}>
-                  {executive_summary}
+              <span className="text-lg">{synthesis?.executive_narrative ? '✨' : '💡'}</span>
+              <div className="flex-1">
+                {synthesis?.executive_narrative && (
+                  <div className="text-xs font-medium text-purple-600 mb-1">AI-Generated Insight</div>
+                )}
+                <p className={`text-gray-700 leading-relaxed ${!showFullSummary && 'line-clamp-3'}`}>
+                  {narrativeText}
                 </p>
-                {executive_summary.length > 150 && (
+                {narrativeText.length > 200 && (
                   <button
                     onClick={() => setShowFullSummary(!showFullSummary)}
                     className="text-blue-600 text-sm font-medium mt-1 hover:underline"