Address PR review: dedicated download secret, shared constants, strip filePath, streaming zip

- jwt.ts: Use JWT_DOWNLOAD_SECRET instead of JWT_SECRET for download tokens
- audio-formats.ts: Add EBOOK_EXTENSIONS export alongside AUDIO_EXTENSIONS
- request-statuses.ts: New shared COMPLETED_STATUSES constant used across requests API, download route, and RequestCard
- requests/route.ts: Import COMPLETED_STATUSES; strip filePath from audiobook in API response
- download/route.ts: Import format/status constants; add archiver dependency and replace adm-zip with streaming archiver for multi-file zips
- RequestCard.tsx: Use shared COMPLETED_STATUSES constant

package.json

@@ -18,7 +18,9 @@
   "dependencies": {
     "@heroicons/react": "^2.2.0",
     "@prisma/client": "^6.19.0",
+    "@types/archiver": "^7.0.0",
     "adm-zip": "^0.5.16",
+    "archiver": "^7.0.1",
     "axios": "^1.7.2",
     "bcrypt": "^5.1.1",
     "bull": "^4.12.0",
@@ -43,9 +45,9 @@
   "devDependencies": {
     "@tailwindcss/postcss": "^4",
     "@testing-library/jest-dom": "^6.9.1",
-    "@types/adm-zip": "^0.5.6",
     "@testing-library/react": "^16.3.1",
     "@testing-library/user-event": "^14.6.1",
+    "@types/adm-zip": "^0.5.6",
     "@types/bcrypt": "^5.0.2",
     "@types/bull": "^4.10.0",
     "@types/jsonwebtoken": "^9.0.6",