fix: send Clear-Site-Data on /__reset for full browser nuke

caches.delete() only clears service-worker managed caches — the
browser's own HTTP cache can still serve stale or corrupted chunk
responses. Setting Clear-Site-Data tells the browser itself to drop
cookies, cached responses, storage, and service worker registrations
for the origin, which is what's actually needed to unstick a PWA
with a bad cached chunk.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

search-app/server.js

@@ -123,6 +123,10 @@ const server = http.createServer((req, res) => {
         res.writeHead(200, {
             'Content-Type': 'text/html; charset=utf-8',
             'Cache-Control': 'no-store, no-cache, must-revalidate',
+            // Clear-Site-Data tells the browser itself to drop cookies,
+            // cached responses, local storage, and SW registrations for
+            // this origin — far more thorough than the JS-side caches.delete.
+            'Clear-Site-Data': '"cache", "storage", "executionContexts"',
             'Service-Worker-Allowed': '/'
         });
         res.end(RESET_HTML);