test: export downloadFile, parsePdfFromFile, extractCwdFromJsonl

These three internal helpers are now imported by regression tests
landing in the next commits (PR #1169 follow-up). Pattern matches the
existing normalizeRemoteUrl export in gstack-global-discover.ts which
test/global-discover.test.ts already imports side-effect-free.

No change to runtime behavior; gstack has no public package entrypoint
that would re-export these, so the in-repo surface is unchanged for
callers.

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

browse/src/security-classifier.ts

@@ -135,7 +135,7 @@ export function getClassifierStatus(): ClassifierStatus {
 
 // ─── Model download + staging ────────────────────────────────
 
-async function downloadFile(url: string, dest: string): Promise<void> {
+export async function downloadFile(url: string, dest: string): Promise<void> {
   const res = await fetch(url);
   if (!res.ok || !res.body) {
     throw new Error(`Failed to fetch ${url}: ${res.status} ${res.statusText}`);