refactor: replace mcp-go with the official MCP Go SDK (#223)

## Summary

Replace `github.com/mark3labs/mcp-go` with the official
`github.com/modelcontextprotocol/go-sdk v1.7.0`.

All 54 existing tools, scopes, CLI, `stdio` and HTTP (`/mcp`) modes, and
per-request authentication remain supported. This PR is limited to the SDK
equivalence migration; the stateless 2026 HTTP transport is deferred to a
follow-up PR.

## Verification

- Tool definitions were compared with `main` and matched for all 54 tools.
- `make lint`, `make fmt`, `go test -count=1 -race ./...`, `make build`, and
  `make tidy` pass.

---------

Co-authored-by: bircni <bircni@icloud.com>
Co-authored-by: silverwind <me@silverwind.io>
Reviewed-on: https://gitea.com/gitea/gitea-mcp/pulls/223
Reviewed-by: silverwind <2021+silverwind@noreply.gitea.com>
Reviewed-by: bircni <bircni@icloud.com>
Co-authored-by: Bo-Yi Wu <appleboy.tw@gmail.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)
 				}
 			}
 		})