Fix Electron production CSS not loading under file://.

Strip crossorigin from the built index so stylesheets apply in the packaged app, and use a relative manifest path for the same reason.

vite.config.js

@@ -136,6 +136,21 @@ function servePublicAssets() {
 }
 
 // CORS proxy for Matrix homeservers during development
+/**
+ * Vite adds crossorigin to module/CSS tags when base is relative (./).
+ * Electron serves the build via file:// — those assets then fail CORS checks
+ * and the app renders with browser defaults (black text, broken spacing).
+ */
+function stripCrossoriginForFileProtocol() {
+  return {
+    name: 'strip-crossorigin-for-file-protocol',
+    apply: 'build',
+    transformIndexHtml(html) {
+      return html.replace(/\s+crossorigin/g, '');
+    },
+  };
+}
+
 function corsProxyMiddleware() {
   return {
     name: 'vite-plugin-cors-proxy',
@@ -228,6 +243,7 @@ export default defineConfig({
     },
   },
   plugins: [
+    stripCrossoriginForFileProtocol(),
     corsProxyMiddleware(), // Add CORS proxy for development
     serverMatrixSdkCryptoWasm('/node_modules/.vite/deps/pkg/matrix_sdk_crypto_wasm_bg.wasm'),
     serveGifWorker(),