feat(theme): add tool_output color to themes

- Added a `tool_output` color to the `Theme` struct.
- Updated all built-in themes to include the new color.
- Modified the TUI to use the `tool_output` color for rendering tool output.

crates/owlen-core/src/mcp/client.rs

@@ -15,6 +15,12 @@ pub trait McpClient: Send + Sync {
 /// Placeholder for a client that connects to a remote MCP server.
 pub struct RemoteMcpClient;
 
+impl RemoteMcpClient {
+    pub fn new() -> Result<Self> {
+        Ok(Self)
+    }
+}
+
 #[async_trait]
 impl McpClient for RemoteMcpClient {
     async fn list_tools(&self) -> Result<Vec<McpToolDescriptor>> {