test: Vitest test infrastructure + 52 unit tests for matching engine

Install vitest, @vitest/coverage-v8, jsdom, @testing-library/react/jest-dom.
Add test / test:watch / test:coverage scripts to package.json.

Three test suites covering the business-critical scoring pipeline:

scoreCalculator.test.ts (28 tests)
- calcDataQualityModifier: all 5 boundary thresholds (+5 / 0 / -5 / -10 / -15)
- calcConfidenceModifier: verified/external/maison-work/future + low-conf stacking
- applyHardFilters: pass, wrong asset type, area tolerance, budget exclusion, OCCUPIED penalty, excluded city
- calculateScore: strong match ≥85, weak match <50, excluded=0, determinism,
  formula verification, DQ+confidence direction, occupied 25-point penalty,
  positive factors, allHardFactors completeness

rankingEngine.test.ts (10 tests)
- matchStrengthFromScore: STRONG/MODERATE/WEAK boundaries (78/52)
- rankMatches: score sort, type tiebreak (VERIFIED > EXTERNAL), confidence tiebreak
- buildFullMatch: all explainability fields, SHORTLIST+CONTACT for strong match,
  SCHEDULE for future signals, uncertainty indicators

matchCardAdapter.test.ts (14 tests)
- VERIFIED_PORTFOLIO: resultType, title, locationLabel, matchScore, scoreBreakdown,
  no disclaimer, reasons from positiveFactors, actions passthrough
- FUTURE_AVAILABILITY: resultType, disclaimer always present, signalProbability,
  signalQuality HIGH for probability >= 0.70

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

package.json

@@ -7,7 +7,10 @@
     "dev": "vite",
     "build": "tsc -b && vite build",
     "lint": "eslint .",
-    "preview": "vite preview"
+    "preview": "vite preview",
+    "test": "vitest run",
+    "test:watch": "vitest",
+    "test:coverage": "vitest run --coverage"
   },
   "dependencies": {
     "@dnd-kit/core": "^6.3.1",
@@ -30,18 +33,23 @@
   "devDependencies": {
     "@eslint/js": "^10.0.1",
     "@tailwindcss/vite": "^4.3.0",
+    "@testing-library/jest-dom": "^6.9.1",
+    "@testing-library/react": "^16.3.2",
     "@types/leaflet": "^1.9.21",
     "@types/node": "^24.12.3",
     "@types/react": "^19.2.14",
     "@types/react-dom": "^19.2.3",
     "@vitejs/plugin-react": "^6.0.1",
+    "@vitest/coverage-v8": "^4.1.7",
     "eslint": "^10.3.0",
     "eslint-plugin-react-hooks": "^7.1.1",
     "eslint-plugin-react-refresh": "^0.5.2",
     "globals": "^17.6.0",
+    "jsdom": "^29.1.1",
     "tailwindcss": "^4.3.0",
     "typescript": "~6.0.2",
     "typescript-eslint": "^8.59.2",
-    "vite": "^8.0.12"
+    "vite": "^8.0.12",
+    "vitest": "^4.1.7"
   }
 }