test(05-01): add unit tests for Y-flip coordinate conversion formula

- Created src/lib/pdf/__tests__/prepare-document.test.ts with 10 test cases
- Tests verify Y-axis flip: screenY=0 → pdfY≈792, screenY=792 → pdfY≈0
- Tests verify scale-invariance at both 1:1 and 50% zoom ratios
- Installed jest, ts-jest, @types/jest and added jest config to package.json
- All 10 tests pass

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

teressa-copeland-homes/package.json

@@ -30,10 +30,15 @@
     "react-pdf": "^10.4.1",
     "zod": "^4.3.6"
   },
+  "jest": {
+    "preset": "ts-jest",
+    "testEnvironment": "node"
+  },
   "devDependencies": {
     "@tailwindcss/postcss": "^4",
     "@types/adm-zip": "^0.5.8",
     "@types/bcryptjs": "^2.4.6",
+    "@types/jest": "^30.0.0",
     "@types/node": "^20",
     "@types/nodemailer": "^7.0.11",
     "@types/react": "^19",
@@ -42,8 +47,10 @@
     "drizzle-kit": "^0.31.10",
     "eslint": "^9",
     "eslint-config-next": "16.2.0",
+    "jest": "^29.7.0",
     "playwright": "^1.58.2",
     "tailwindcss": "^4",
+    "ts-jest": "^29.4.6",
     "tsx": "^4.21.0",
     "typescript": "^5"
   }