Make the vitest 4 upgrade pass CI

The bare `vitest` bump fails `yarn install` with "could not find a copy
of vite to link in node_modules/vitest/node_modules". vitest 4 now lists
`vite` as a direct dependency (^6 || ^7 || ^8), so yarn 1 resolves a
second vite major alongside the repo's hoisted vite ^6.0.1 and chokes on
the nested link. Pin `vite` to ^6.0.1 in `resolutions` so the whole tree
shares a single vite 6.x (in range for vitest, and what the build used).

Also:
- Bump `@vitest/coverage-v8` and `@vitest/ui` to ^4.1.0 to match the
  vitest 4 runtime (Dependabot only bumped `vitest` itself).
- Add "node" to the core package's tsconfig `types`. vitest 4's
  `vitest/globals` no longer transitively pulls in @types/node, which
  broke type-checking of test files (`import assert from 'assert'`).
  The datetime and mcp-server tsconfigs already list "node".

yarn install --frozen-lockfile, lint, build, type-check, the full test
suite, and coverage all pass locally.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: Sander Toonen

package.json

@@ -36,6 +36,7 @@
     "vitest": "^4.1.0"
   },
   "resolutions": {
-    "ip-address": "^10.1.1"
+    "ip-address": "^10.1.1",
+    "vite": "^6.0.1"
   }
 }

packages/expreszo-datetime/package.json

@@ -47,7 +47,7 @@
   },
   "devDependencies": {
     "@types/luxon": "^3.4.0",
-    "@vitest/coverage-v8": "^3.2.4",
+    "@vitest/coverage-v8": "^4.1.0",
     "@types/node": "^24.5.2",
     "cross-env": "^7.0.3",
     "rimraf": "^5.0.10",

packages/expreszo-mcp-server/package.json

@@ -48,7 +48,7 @@
   },
   "devDependencies": {
     "@types/node": "^24.5.2",
-    "@vitest/coverage-v8": "^3.2.4",
+    "@vitest/coverage-v8": "^4.1.0",
     "cross-env": "^7.0.3",
     "rimraf": "^5.0.10",
     "tsx": "^4.20.5",

packages/expreszo/package.json

@@ -120,8 +120,8 @@
     "@rollup/plugin-typescript": "^12.1.4",
     "@types/node": "^24.5.2",
     "@typescript/native-preview": "^7.0.0-dev.20250920.1",
-    "@vitest/coverage-v8": "^3.2.4",
-    "@vitest/ui": "^3.2.4",
+    "@vitest/coverage-v8": "^4.1.0",
+    "@vitest/ui": "^4.1.0",
     "cross-env": "^7.0.3",
     "eslint": "^9.15.0",
     "eslint-plugin-import": "^2.32.0",

packages/expreszo/tsconfig.json

@@ -4,7 +4,7 @@
     "outDir": "./dist",
     "rootDir": "./",
     "tsBuildInfoFile": "./dist/.tsbuildinfo",
-    "types": ["vitest/globals"]
+    "types": ["vitest/globals", "node"]
   },
   "include": [
     "src/**/*",