feat(js): m04 random and spawn with fixtures and tests

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

fixtures/m04-new-game.json

@@ -0,0 +1,73 @@
+{
+  "function": "newGame",
+  "cases": [
+    {
+      "name": "seed-0",
+      "args": [
+        0
+      ],
+      "expected": {
+        "width": 20,
+        "height": 20,
+        "snake": [
+          {
+            "x": 10,
+            "y": 10
+          },
+          {
+            "x": 9,
+            "y": 10
+          },
+          {
+            "x": 8,
+            "y": 10
+          }
+        ],
+        "dir": "Right",
+        "nextDir": "Right",
+        "apple": {
+          "x": 18,
+          "y": 13
+        },
+        "seed": 1831565813,
+        "score": 0,
+        "status": "Playing",
+        "frame": 0
+      }
+    },
+    {
+      "name": "seed-42",
+      "args": [
+        42
+      ],
+      "expected": {
+        "width": 20,
+        "height": 20,
+        "snake": [
+          {
+            "x": 10,
+            "y": 10
+          },
+          {
+            "x": 9,
+            "y": 10
+          },
+          {
+            "x": 8,
+            "y": 10
+          }
+        ],
+        "dir": "Right",
+        "nextDir": "Right",
+        "apple": {
+          "x": 1,
+          "y": 9
+        },
+        "seed": 1831565855,
+        "score": 0,
+        "status": "Playing",
+        "frame": 0
+      }
+    }
+  ]
+}