refactor!: replace mcp-go with the official MCP Go SDK

- Swap the mark3labs MCP dependency for modelcontextprotocol/go-sdk v1.7.0
- Add a declarative tool definition and JSON Schema builder to the tool package
- Adapt registered tools to the official low-level handler, recovering panics and mapping failures to JSON-RPC errors
- Narrow tool handlers to take a plain argument map instead of an SDK request type
- Rewire stdio and HTTP transports onto the official server, moving Authorization parsing into receiving middleware
- Add a golden contract test that locks the exposed tool schemas, plus SDK integration and helper tests
- Add a test target and run it in the pull request workflow

BREAKING CHANGE: The exported helpers change signature. Tool.RegisterRead and
Tool.RegisterWrite now take tool.ServerTool instead of server.ServerTool, and the
annotation constructors return *mcp.ToolAnnotations from the official SDK. Callers
must build tool definitions with tool.NewDefinition and handlers with the
func(context.Context, map[string]any) signature.

The 30-second SSE heartbeat is removed because the official SDK has no equivalent.
ServerOptions.KeepAlive is deliberately not used as a substitute, since it sends MCP
ping requests and ping is removed in protocol 2026. HTTP stays stateless=false, so
new clients negotiate at most 2025-11-25.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

operation/search/search_test.go

@@ -4,13 +4,13 @@ import (
 	"slices"
 	"testing"
 
-	"github.com/mark3labs/mcp-go/mcp"
+	"github.com/modelcontextprotocol/go-sdk/mcp"
 )
 
 func TestSearchToolsRequiredFields(t *testing.T) {
 	tests := []struct {
 		name     string
-		tool     mcp.Tool
+		tool     *mcp.Tool
 		required []string
 	}{
 		{
@@ -32,9 +32,11 @@ func TestSearchToolsRequiredFields(t *testing.T) {
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
+			inputSchema := tt.tool.InputSchema.(map[string]any)
+			required, _ := inputSchema["required"].([]string)
 			for _, field := range tt.required {
-				if !slices.Contains(tt.tool.InputSchema.Required, field) {
-					t.Errorf("tool %s: expected %q to be required, got required=%v", tt.name, field, tt.tool.InputSchema.Required)
+				if !slices.Contains(required, field) {
+					t.Errorf("tool %s: expected %q to be required, got required=%v", tt.name, field, required)
 				}
 			}
 		})