chore(core-typescript): put its TS sources under the typecheck gate

The package's vitest base configs were outside every gate — no tsconfig
and no typecheck script meant tsc never saw them. Add a tsconfig with
allowImportingTsExtensions (vitest.base.jsdom imports ./vitest.base.node.ts
by extension) and an explicit include of the base configs + vitest
config, plus the typescript/@types/node devDeps to run it. (S6)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

packages/core-typescript/package.json

@@ -12,10 +12,13 @@
     "./vitest.base.jsdom": "./vitest.base.jsdom.ts"
   },
   "scripts": {
-    "test": "vitest run"
+    "test": "vitest run",
+    "typecheck": "tsc --noEmit"
   },
   "devDependencies": {
+    "@types/node": "^22.15.0",
     "@vitest/coverage-v8": "^3.2.7",
+    "typescript": "^5.8.0",
     "vitest": "^3.2.7"
   }
 }

packages/core-typescript/tsconfig.json

@@ -0,0 +1,15 @@
+{
+  "extends": "./base.json",
+  "compilerOptions": {
+    "rootDir": ".",
+    "noEmit": true,
+    "allowImportingTsExtensions": true,
+    "types": ["node"]
+  },
+  "include": [
+    "vitest.base.ts",
+    "vitest.base.node.ts",
+    "vitest.base.jsdom.ts",
+    "vitest.config.ts"
+  ]
+}