Use redirect: manual to let browser handle redirects

Bun's fetch was following Go's 303 redirects internally, which
caused ECONNRESET errors during the auto-login redirect chain.
Let the browser handle redirects instead.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/proxy.ts

@@ -28,6 +28,7 @@ export function createProxy(isHealthy: () => boolean, isRunning: () => boolean)
       method: req.method,
       headers: req.headers,
       body,
+      redirect: 'manual',
     }).then((r) => {
       // Bun auto-decompresses gzip but leaves content-encoding header.
       // Strip it so the next proxy layer doesn't try to decompress again.