examples: add a 'listeverything' client example, and reorganize

Add a client example that lists all features on a stdio server. Since
this is our first client example, organize examples by client / server
-- otherwise it is too difficult to find client examples.

For #33

examples/server/sse/main.go

@@ -0,0 +1,70 @@
+// Copyright 2025 The Go MCP SDK Authors. All rights reserved.
+// Use of this source code is governed by an MIT-style
+// license that can be found in the LICENSE file.
+
+package main
+
+import (
+	"context"
+	"flag"
+	"fmt"
+	"log"
+	"net/http"
+	"os"
+
+	"github.com/modelcontextprotocol/go-sdk/mcp"
+)
+
+var (
+	host = flag.String("host", "localhost", "host to listen on")
+	port = flag.String("port", "8080", "port to listen on")
+)
+
+type SayHiParams struct {
+	Name string `json:"name"`
+}
+
+func SayHi(ctx context.Context, cc *mcp.ServerSession, params *mcp.CallToolParamsFor[SayHiParams]) (*mcp.CallToolResultFor[any], error) {
+	return &mcp.CallToolResultFor[any]{
+		Content: []mcp.Content{
+			&mcp.TextContent{Text: "Hi " + params.Arguments.Name},
+		},
+	}, nil
+}
+
+func main() {
+	flag.Usage = func() {
+		fmt.Fprintf(os.Stderr, "Usage: %s [options]\n\n", os.Args[0])
+		fmt.Fprintf(os.Stderr, "This program runs MCP servers over SSE HTTP.\n\n")
+		fmt.Fprintf(os.Stderr, "Options:\n")
+		flag.PrintDefaults()
+		fmt.Fprintf(os.Stderr, "\nEndpoints:\n")
+		fmt.Fprintf(os.Stderr, "  /greeter1 - Greeter 1 service\n")
+		fmt.Fprintf(os.Stderr, "  /greeter2 - Greeter 2 service\n")
+		os.Exit(1)
+	}
+	flag.Parse()
+
+	addr := fmt.Sprintf("%s:%s", *host, *port)
+
+	server1 := mcp.NewServer(&mcp.Implementation{Name: "greeter1"}, nil)
+	mcp.AddTool(server1, &mcp.Tool{Name: "greet1", Description: "say hi"}, SayHi)
+
+	server2 := mcp.NewServer(&mcp.Implementation{Name: "greeter2"}, nil)
+	mcp.AddTool(server2, &mcp.Tool{Name: "greet2", Description: "say hello"}, SayHi)
+
+	log.Printf("MCP servers serving at %s", addr)
+	handler := mcp.NewSSEHandler(func(request *http.Request) *mcp.Server {
+		url := request.URL.Path
+		log.Printf("Handling request for URL %s\n", url)
+		switch url {
+		case "/greeter1":
+			return server1
+		case "/greeter2":
+			return server2
+		default:
+			return nil
+		}
+	})
+	log.Fatal(http.ListenAndServe(addr, handler))
+}