Add Android node foundation with FCM push support

docs/api/PROTOCOL.md

@@ -669,7 +669,7 @@ Publish companion/node runtime status metadata (for example macOS menu-bar heart
 
 #### `node.push_token.set`
 
-Register a node push token (currently APNs) for companion delivery routing.
+Register a node push token (APNs or FCM) for companion delivery routing.
 Requires `server.nodes.push.enabled: true`.
 
 **Request:**
@@ -678,10 +678,8 @@ Requires `server.nodes.push.enabled: true`.
   "id": 13,
   "method": "node.push_token.set",
   "params": {
-    "provider": "apns",
-    "token": "abcd1234abcd1234abcd1234abcd1234",
-    "topic": "com.example.flynn",
-    "environment": "sandbox"
+    "provider": "fcm",
+    "token": "fcm_abcdefghijklmnopqrstuvwxyz123456"
   }
 }
 ```