fix: remove background rect from main map SVG

Remove the background rect from the main map SVG (not magnifier).
This was causing the mispositioned blue rectangle to appear on the left.

The map container already has its own background styling, so the SVG
rect is unnecessary.

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

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

apps/web/src/arcade-games/know-your-world/components/MapRenderer.tsx

@@ -1454,9 +1454,6 @@ export function MapRenderer({
           aspectRatio: `${viewBoxWidth} / ${viewBoxHeight}`,
         }}
       >
-        {/* Background */}
-        <rect x="0" y="0" width="100%" height="100%" fill={isDark ? '#111827' : '#f3f4f6'} />
-
         {/* Render all regions (included + excluded) */}
         {[...mapData.regions, ...excludedRegions].map((region) => {
           const isExcluded = excludedRegionIds.has(region.id)