fix(backend): Round heatmap values to 2 decimal places

Prevents long decimal numbers like 37.805740635007325 from displaying
in the UI. Now shows clean values like 37.81.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

backend/src/multi-state/state-query-service.ts

@@ -824,10 +824,11 @@ export class StateQueryService {
 
     const result = await this.pool.query(query, params);
     // Parse numeric values from strings (PostgreSQL returns bigint as string)
+    // Round to 2 decimal places for display
     return result.rows.map((row: any) => ({
       state: row.state,
       stateName: row.stateName,
-      value: row.value !== null ? parseFloat(row.value) : 0,
+      value: row.value !== null ? Math.round(parseFloat(row.value) * 100) / 100 : 0,
       label: row.label,
     }));
   }