feat: add PDF export for DevCard (issue #615)

- Add useExportPDF hook using html2canvas + jsPDF
- Support US (3.5x2in) and EU (85x55mm) business card sizes
- Add Export as PDF buttons on CardPage below connections
- Filename auto-generated as DevCard_<Name>.pdf

Author: Jai-Shankar1033

apps/web/package.json

@@ -11,6 +11,8 @@
     "test": "vitest run"
   },
   "dependencies": {
+    "html2canvas": "^1.4.1",
+    "jspdf": "^4.2.1",
     "react": "^19.2.6",
     "react-dom": "^19.2.6",
     "react-router-dom": "^7.6.2"