feedback5 R6: add a small checkJs slice and core typedefs

tsc checks shared (except protocol.js and bandBonds.js), the sim rng/dir/constants helpers, and types/core.js. strict stays off. types/README.md says how to widen the slice.

package-lock.json

@@ -21,7 +21,8 @@
         "@eslint/js": "^10.0.1",
         "eslint": "^10.12.0",
         "globals": "^17.13.0",
-        "puppeteer-core": "^25.12.0"
+        "puppeteer-core": "^25.12.0",
+        "typescript": "^5.9.2"
       },
       "engines": {
         "node": ">=22"
@@ -2334,6 +2335,20 @@
       "engines": {
         "node": ">= 18"
       }
+    },
+    "node_modules/typescript": {
+      "version": "5.9.3",
+      "resolved": "https://registry.npmjs.org/typescript/-/typescript-5.9.3.tgz",
+      "integrity": "sha512-jl1vZzPDinLr9eUt3J/t7V6FgNEw9QjvBPdysz9KfQDD41fQrC2Y4vKQdiaUpFT4bXlb1RHhLpp8wtm6M5TgSw==",
+      "dev": true,
+      "license": "Apache-2.0",
+      "bin": {
+        "tsc": "bin/tsc",
+        "tsserver": "bin/tsserver"
+      },
+      "engines": {
+        "node": ">=14.17"
+      }
     }
   }
 }