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>

vitest.config.ts

@@ -0,0 +1,17 @@
+import { defineConfig } from 'vitest/config'
+import react from '@vitejs/plugin-react'
+
+export default defineConfig({
+  plugins: [react()],
+  test: {
+    environment: 'jsdom',
+    setupFiles: ['./src/test/setup.ts'],
+    include: ['src/**/*.{test,spec}.{ts,tsx}'],
+    coverage: {
+      provider: 'v8',
+      reporter: ['text', 'html'],
+      include: ['src/features/**', 'src/lib/**'],
+      exclude: ['src/**/*.test.*', 'src/**/*.spec.*'],
+    },
+  },
+})