feat(folio-webApp): add main entrypoint and index.html

main.kt mirrors the iOS entry point: builds DriverFactory + AppGraph
factory, hooks browser back-gesture into WebBackGesture, then mounts
the shared App composable into ComposeViewport.

examples/folio/app/webApp/src/wasmJsMain/resources/index.html

@@ -0,0 +1,16 @@
+<!DOCTYPE html>
+<html lang="en">
+<head>
+    <meta charset="UTF-8">
+    <meta name="viewport" content="width=device-width, initial-scale=1, viewport-fit=cover">
+    <title>Folio</title>
+    <style>
+        html, body { margin: 0; padding: 0; height: 100%; background: #000; color: #fff; font-family: system-ui, sans-serif; }
+        #app { height: 100%; }
+    </style>
+</head>
+<body>
+<div id="app"></div>
+<script src="composeApp.js"></script>
+</body>
+</html>