fix: use absolute path for GeoJSON in constituency map

- Change from relative path to absolute path
- Fixes map not loading when displayed in iframe
- Path: /assets/posts/scottish-budget-2026-income-tax-threshold-uplift/uk_constituencies_2024.geojson

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

Author: vahid-ahmadi

app/public/assets/posts/scottish-budget-2026-income-tax-threshold-uplift/constituency_map_income_tax_threshold_uplift.html

@@ -358,7 +358,7 @@
 
         // Load GeoJSON and initialize map
         async function initMap() {
-            const geoData = await d3.json("uk_constituencies_2024.geojson");
+            const geoData = await d3.json("/assets/posts/scottish-budget-2026-income-tax-threshold-uplift/uk_constituencies_2024.geojson");
 
             const scottishFeatures = geoData.features.filter(f =>
                 f.properties.GSScode && f.properties.GSScode.startsWith('S')