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/wiki/wiki_test.go

@@ -11,8 +11,6 @@ import (
 
 	mcpContext "gitea.com/gitea/gitea-mcp/pkg/context"
 	"gitea.com/gitea/gitea-mcp/pkg/flag"
-
-	"github.com/mark3labs/mcp-go/mcp"
 )
 
 func TestWikiWriteBase64Encoding(t *testing.T) {
@@ -54,10 +52,7 @@ func TestWikiWriteBase64Encoding(t *testing.T) {
 				"title":    "TestPage",
 			}
 
-			req := mcp.CallToolRequest{}
-			req.Params.Arguments = args
-
-			result, err := wikiWriteFn(ctx, req)
+			result, err := wikiWriteFn(ctx, args)
 			if err != nil {
 				t.Fatalf("wikiWriteFn() error: %v", err)
 			}