Add Protocol constants and enable buildConfig generation

app/build.gradle.kts

@@ -38,6 +38,7 @@ android {
     
     buildFeatures {
         viewBinding = true
+        buildConfig = true
     }
 }
 

app/src/main/java/com/inou/clawdnode/protocol/Protocol.kt

@@ -0,0 +1,19 @@
+package com.inou.clawdnode.protocol
+
+/**
+ * Clawdbot Gateway Protocol constants.
+ * Values from clawdbot/gateway/protocol/client-info.js
+ */
+object Protocol {
+    // Gateway client identifier for Android app
+    const val CLIENT_ID = "clawdbot-android"
+    
+    // Client mode - "node" for ClawdNode companion apps
+    const val MODE = "node"
+    
+    // Platform identifier
+    const val PLATFORM = "android"
+    
+    // Role for node connections
+    const val ROLE = "node"
+}