FEAT: Add Vega Char Visualizer Renderer

### FEAT: Add Vega Char Visualizer Renderer

Feature required in https://github.com/open-webui/open-webui/discussions/18022

Added npm vega lib to package.json
Added function for visualization renderer to src/libs/utils/index.ts
Added logic to src/lib/components/chat/Messages/CodeBlock.svelte

The treatment is similar as for mermaid diagrams.

Reference: https://vega.github.io/vega/

src/lib/utils/index.ts

@@ -1596,3 +1596,16 @@ export const renderMermaidDiagram = async (code: string) => {
 		return '';
 	}
 };
+
+export const renderVegaVisualization = async (spec: string) => {
+	try {
+		const vega = await import('vega');
+		const parsedSpec = JSON.parse(spec);
+		const view = new vega.View(vega.parse(parsedSpec), { renderer: 'none' });
+		const svg = await view.toSVG();
+		return svg;
+	} catch (error) {
+		console.log('Failed to render Vega visualization:', error);
+		return '';
+	}
+};