fix: make the base path relative

Adjusts Vite configuration to set the base path to `./` in order to accommodate the deployment
on GitHub Pages. The demo is served under `/pillarbox-web-demo` instead of the root path, using
relative paths in the generated build ensures proper page serving.

Other changes: Adds map source generation.

vite.config.js

@@ -0,0 +1,13 @@
+import { defineConfig } from 'vite';
+
+/**
+ * Vite configuration file.
+ *
+ * @see https://vitejs.dev/config/
+ */
+export default defineConfig({
+  base: './',
+  build: {
+    sourcemap: true
+  }
+});