feat: add networking module with TCP Socket/Server and example applications

Implement a full-featured `net` module supporting TCP `Socket` and `Server` classes via libuv, including example applications (chat server, echo server, HTTP client/server, file explorer, system dashboard) and benchmark scripts (fibonacci, n-body). Add GEMINI.md project documentation and Stderr class to io module.

example/echo_server.wren

@@ -0,0 +1,25 @@
+import "net" for Server
+import "scheduler" for Scheduler
+
+var port = 9090
+var server = Server.bind("0.0.0.0", port)
+System.print("Echo Server running on port %(port)")
+
+while (true) {
+  var socket = server.accept()
+  System.print("New connection accepted")
+  
+  Fiber.new {
+    var socket_ = socket // Capture variable
+    while (true) {
+      var data = socket_.read()
+      if (data == null) {
+          break
+      }
+      System.print("Received: %(data.count) bytes")
+      socket_.write(data)
+    }
+    System.print("Connection closed")
+    socket_.close()
+  }.call()
+}