feat(kotlin-host): add structuredContent support

Include structuredContent from CallToolResult in the JSON passed to AppBridge.
This enables apps to receive structured data from tool results.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: ochafik

examples/basic-host-kotlin/src/main/kotlin/com/example/mcpappshost/McpHostViewModel.kt

@@ -283,6 +283,10 @@ class McpHostViewModel : ViewModel() {
                                         }
                                     })
                                     put("isError", JsonPrimitive(callResult.isError ?: false))
+                                    // Include structuredContent if present
+                                    callResult.structuredContent?.let { sc ->
+                                        put("structuredContent", sc)
+                                    }
                                 }
                             )
                             updateToolCall(toolCall.id) { it.copy(
@@ -378,6 +382,10 @@ class McpHostViewModel : ViewModel() {
                     }
                 })
                 put("isError", JsonPrimitive(callResult.isError ?: false))
+                // Include structuredContent if present
+                callResult.structuredContent?.let { sc ->
+                    put("structuredContent", sc)
+                }
             }
         )