Add deterministic-tests workspace

Scripted multi-client harness against a real server (~110 scenario
tests, server-control, managed-websocket, test-runner). Wires the new
package into frontend/package.json workspaces and the lint script.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/deterministic-tests/tsconfig.json

@@ -0,0 +1,12 @@
+{
+    "compilerOptions": {
+        "baseUrl": ".",
+        "strict": true,
+        "target": "ES2022",
+        "module": "CommonJS",
+        "esModuleInterop": true,
+        "lib": ["DOM", "ES2024"],
+        "moduleResolution": "node"
+    },
+    "exclude": ["./dist"]
+}