fix: redirect tracing logs to stderr to keep stdout clean for MCP JSON

tracing_subscriber::fmt::init() defaults to stdout, contaminating the
MCP JSON-RPC stream and causing Claude Code and Windsurf to fail the
initialize handshake with "failed to reconnect".

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/main.rs

@@ -78,7 +78,9 @@ pub struct ToolCapabilities {
 
 #[tokio::main]
 async fn main() -> Result<()> {
-    tracing_subscriber::fmt::init();
+    tracing_subscriber::fmt()
+        .with_writer(std::io::stderr)
+        .init();
     
     let cli = Cli::parse();