feat(runtime): add Service Worker with .ts/.tsx fetch interception

- Intercept requests ending in .ts or .tsx at the fetch event level
- Transpile TypeScript source via transpiler module on the fly
- Return transpiled JS with correct application/javascript MIME type
- Pass through all non-TypeScript requests unchanged

Author: singhjashanjot

packages/runtime/src/sw.ts

@@ -0,0 +1,22 @@
+declare const self: ServiceWorkerGlobalScope
+
+import { transpile } from './transpiler.js'
+
+async function handleFetch(event: FetchEvent): Promise<Response> {
+  const url = new URL(event.request.url)
+
+  if (url.pathname.endsWith('.ts') || url.pathname.endsWith('.tsx')) {
+    const response = await fetch(event.request)
+    const source = await response.text()
+    const transpiled = await transpile(source, url.pathname)
+    return new Response(transpiled, {
+      headers: { 'Content-Type': 'application/javascript' },
+    })
+  }
+
+  return fetch(event.request)
+}
+
+self.addEventListener('fetch', (event: FetchEvent) => {
+  event.respondWith(handleFetch(event))
+})