fix: replace pdf-parse with direct pdfjs-dist to fix DOMMatrix error in production

pdf-parse v2 depends on @napi-rs/canvas (native module) which fails in
Next.js standalone Docker builds — native binaries aren't traced/copied
to the standalone output, causing DOMMatrix is not defined at runtime.

Replaced pdf-parse entirely with pdfjs-dist legacy build which works
natively in Node.js without canvas or DOM API dependencies:

- New src/lib/pdf.ts: extractTextFromPdf() using pdfjs-dist/legacy/build
- Worker file explicitly imported so Next.js file tracer includes it
- Updated all call sites: documents, norms/parse, contracts
- Removed pdf-parse from dependencies, added pdfjs-dist directly
- Changed serverExternalPackages from pdf-parse to pdfjs-dist

Verified: build succeeds, both pdf.mjs and pdf.worker.mjs present in
.next/standalone, text extraction works in standalone context.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

package.json

@@ -18,7 +18,7 @@
     "mammoth": "^1.12.0",
     "next": "16.2.3",
     "next-auth": "^4.24.13",
-    "pdf-parse": "^2.4.5",
+    "pdfjs-dist": "^5.4.296",
     "pg": "^8.20.0",
     "react": "19.2.4",
     "react-dom": "19.2.4"