fix(pdf-compress): stream large uploads via busboy instead of arrayBuffer

req.arrayBuffer() fails with 502 on files >100MB because it tries to
buffer the entire body in memory before the route handler runs.

New approach: busboy streams the multipart body directly to a temp file
on disk — never buffers the whole request in memory. Works for any size.

Shared helper: parse-upload.ts (busboy streaming, 500MB limit, fields).
Both local (qpdf) and cloud (iLovePDF) routes refactored to use it.

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

package.json

@@ -12,6 +12,7 @@
     "@prisma/client": "^6.19.2",
     "axios": "^1.13.6",
     "axios-cookiejar-support": "^6.0.5",
+    "busboy": "^1.6.0",
     "class-variance-authority": "^0.7.1",
     "clsx": "^2.1.1",
     "docx": "^9.6.0",
@@ -36,6 +37,7 @@
   },
   "devDependencies": {
     "@tailwindcss/postcss": "^4",
+    "@types/busboy": "^1.5.4",
     "@types/jszip": "^3.4.0",
     "@types/node": "^20",
     "@types/nodemailer": "^7.0.11",