test: add vitest, coverage and mutation gate with availability domain core

Pure logic lives in apps/web/src/domain and must stay at 100% coverage and a
100% mutation score. The first unit is the availability logic for the hero:
parsing, resolving and formatting the next free capacity block.

Vitest is pinned to 4.1.11 because @stryker-mutator/vitest-runner 10.0.0
runs zero tests per mutant under vitest 5 and reports surviving mutants.
ESLint now ignores Stryker, coverage and report output.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

apps/web/package.json

@@ -9,7 +9,8 @@
     "build": "next build --webpack",
     "start": "next start",
     "lint": "eslint app src scripts video",
-    "test": "echo \"No tests configured\"",
+    "test": "vitest run",
+    "test:coverage": "vitest run --coverage",
     "test:links": "tsx ./scripts/test-links.ts",
     "test:file-examples": "tsx ./scripts/test-file-examples-comprehensive.ts",
     "generate-estimate": "tsx ./scripts/generate-estimate.ts",
@@ -21,6 +22,7 @@
     "video:render:all": "npm run video:render:contact && npm run video:render:button",
     "pagespeed:test": "npx tsx ./scripts/pagespeed-sitemap.ts",
     "typecheck": "tsc --noEmit",
+    "test:mutation": "stryker run",
     "check:og": "tsx scripts/check-og-images.ts",
     "check:forms": "tsx scripts/check-forms.ts"
   },
@@ -104,12 +106,16 @@
     "@mintel/next-utils": "^1.9.0",
     "@mintel/tsconfig": "^1.9.0",
     "@next/eslint-plugin-next": "^16.1.6",
+    "@stryker-mutator/core": "^10.0.0",
+    "@stryker-mutator/typescript-checker": "^10.0.0",
+    "@stryker-mutator/vitest-runner": "^10.0.0",
     "@tailwindcss/typography": "^0.5.15",
     "@types/mime-types": "^3.0.1",
     "@types/node": "^25.0.6",
     "@types/nodemailer": "^7.0.10",
     "@types/prismjs": "^1.26.5",
     "@types/qrcode": "^1.5.6",
+    "@vitest/coverage-v8": "^4.1.11",
     "autoprefixer": "^10.4.20",
     "cheerio": "^1.1.2",
     "concurrently": "^9.2.1",
@@ -121,7 +127,8 @@
     "require-extensions": "^0.0.4",
     "tsx": "^4.21.0",
     "typescript": "5.9.3",
-    "typescript-eslint": "^8.54.0"
+    "typescript-eslint": "^8.54.0",
+    "vitest": "^4.1.11"
   },
   "repository": {
     "type": "git",