Fix MCP serve: remove stdin conflict and premature ProjectContext call

Two bugs caused immediate connection close:
1. ProjectContext.find() at startup crashed if cwd wasn't a project root;
   it's not needed here — each tool handler calls it on demand.
2. io.stdin.drain() added a second listener to stdin after stdioChannel
   already subscribed, throwing StateError and killing the process.

The Dart event loop keeps the process alive while stdin has a listener.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

packages/mcp/lib/src/commands/serve_command.dart

@@ -21,21 +21,17 @@ class ServeCommand extends DewCommand {
 
   @override
   Future<void> run() async {
-    final context = await ProjectContext.find();
     final tools = _toolRegistry.allTools;
 
     io.stderr.writeln(
-      'Dew MCP server starting — '
+      'Dew MCP server starting — ${tools.length} tool(s) registered.',
-      '${tools.length} tool(s) registered, '
-      'project root: ${context.root}',
     );
 
+    // stdioChannel subscribes to stdin; do not touch stdin after this point.
+    // The Dart event loop keeps the process alive until the client disconnects.
     DewMcpServer(
       stdioChannel(input: io.stdin, output: io.stdout),
       tools,
     );
-
-    // Keep the process alive until the MCP client closes the connection.
-    await io.stdin.drain<void>();
   }
 }