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/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)
 			}