test: reduce low-memory Vitest pressure (#50652)

* test: reduce low-memory Vitest pressure

Reuse the bundled config baseline inside doc-baseline tests, keep that hotspot out of the shared unit-fast lane, and make OPENCLAW_TEST_PROFILE=low default to process forks instead of vmForks.

* test: keep low-profile vmForks in CI

Scope the low-profile forks fallback to local runs so the existing CI contracts lane keeps its current pool behavior.

test/fixtures/test-parallel.behavior.json

@@ -13,6 +13,10 @@
         "file": "src/infra/git-commit.test.ts",
         "reason": "Mutates process.cwd() and core loader seams."
       },
+      {
+        "file": "src/config/doc-baseline.test.ts",
+        "reason": "Rebuilds bundled config baselines through many channel schema subprocesses; keep out of the shared lane."
+      },
       {
         "file": "extensions/imessage/src/monitor.shutdown.unhandled-rejection.test.ts",
         "reason": "Touches process-level unhandledRejection listeners."