feat(core-*): add Vitest configs + composition tests

core-api: appRouter exposes all 4 feature routers + blog procedure shape.
core-cms: payloadConfig registers all collections + globals.
core-trpc: client + provider exports verified.

Spec: §6.1, §6.6

packages/core-api/package.json

@@ -9,7 +9,8 @@
   "scripts": {
     "build": "tsc --noEmit",
     "lint": "eslint .",
-    "typecheck": "tsc --noEmit"
+    "typecheck": "tsc --noEmit",
+    "test": "vitest run --passWithNoTests"
   },
   "dependencies": {
     "@repo/auth": "workspace:*",
@@ -21,7 +22,9 @@
   },
   "devDependencies": {
     "@repo/core-eslint": "workspace:*",
+    "@repo/core-testing": "workspace:*",
     "@repo/core-typescript": "workspace:*",
-    "@types/node": "^22.0.0"
+    "@types/node": "^22.0.0",
+    "vitest": "^3.0.0"
   }
 }