Fix wealth distribution chart functionality

- Add get_wealth_histogram() method to EconomicModel for histogram data
- Add new API endpoint /simulation/<id>/distribution for chart data
- Extend main data API with include_distribution parameter
- Update real-time progress updates to include distribution data
- Fix frontend updateCharts() to handle wealth distribution chart
- Add distribution data processing in simulation.js
- Update test_charts.py to verify histogram functionality

Resolves issue where wealth distribution chart was not updating during simulations.

app/static/js/simulation.js

@@ -15,7 +15,11 @@ let currentSimulation = {
         totalWealth: [],
         giniCoefficients: [],
         capitalShare: [],
-        top10Share: []
+        top10Share: [],
+        distribution: {
+            labels: [],
+            counts: []
+        }
     }
 };
 
@@ -445,7 +449,11 @@ function resetSimulation() {
             totalWealth: [],
             giniCoefficients: [],
             capitalShare: [],
-            top10Share: []
+            top10Share: [],
+            distribution: {
+                labels: [],
+                counts: []
+            }
         }
     };
     
@@ -596,6 +604,12 @@ function updateSimulationProgress(data) {
         currentSimulation.data.capitalShare.push(data.capital_share || 0);
         currentSimulation.data.top10Share.push(data.wealth_concentration_top10 || 0);
         
+        // Update distribution data if available
+        if (data.distribution && data.distribution.labels && data.distribution.counts) {
+            currentSimulation.data.distribution.labels = data.distribution.labels;
+            currentSimulation.data.distribution.counts = data.distribution.counts;
+        }
+        
         updateCharts();
         updateMetricsDisplay(data);
     }
@@ -619,6 +633,13 @@ function updateCharts() {
         charts.inequality.data.datasets[1].data = currentSimulation.data.top10Share;
         charts.inequality.update('none');
     }
+    
+    // Wealth Distribution Chart
+    if (charts.distribution && currentSimulation.data.distribution.labels.length > 0) {
+        charts.distribution.data.labels = currentSimulation.data.distribution.labels;
+        charts.distribution.data.datasets[0].data = currentSimulation.data.distribution.counts;
+        charts.distribution.update('none');
+    }
 }
 
 /**
@@ -658,7 +679,7 @@ async function onSimulationComplete(data) {
     // Fetch complete simulation data and populate charts
     try {
         const response = await window.MarkovEconomics.utils.apiRequest(
-            `/api/simulation/${currentSimulation.id}/data?include_evolution=true`
+            `/api/simulation/${currentSimulation.id}/data?include_evolution=true&include_distribution=true`
         );
         
         if (response.evolution) {
@@ -669,6 +690,12 @@ async function onSimulationComplete(data) {
             currentSimulation.data.top10Share = response.evolution.top10_shares || [];
             currentSimulation.data.capitalShare = response.evolution.capital_shares || [];
             
+            // Update distribution data
+            if (response.distribution) {
+                currentSimulation.data.distribution.labels = response.distribution.labels;
+                currentSimulation.data.distribution.counts = response.distribution.counts;
+            }
+            
             // Update charts with complete data
             updateCharts();