chore: forbid Node.js builtin imports in frontend source

- Turns on Biome's `correctness/noNodejsModules` for
`oss/frontend/src/**`.
- #2019 imported `node:util` in a frontend file. Type check, unit tests
and the build passed, and the app broke in the browser (fixed in #2029).
This makes that import a lint error.
- Checked against the #2019 version of
`strategy-change-diff-calculation.ts`: lint fails on the import. Current
`main` passes with no hits, so no source changes are needed.
- Scoped to `src` so `vite.config.mts` and the Cypress config can keep
using Node builtins.
- Does not cover a dependency that imports a Node builtin. That still
needs a runtime check.

biome.json

@@ -99,7 +99,14 @@
     },
     {
       "includes": ["frontend/src/**"],
-      "plugins": ["./tracking-shape.grit"]
+      "plugins": ["./tracking-shape.grit"],
+      "linter": {
+        "rules": {
+          "correctness": {
+            "noNodejsModules": "error"
+          }
+        }
+      }
     },
     {
       "includes": [