feat(32.1-01): publish one MCP scope list and call context

- pact gains MemberTokenScopeCatalog, MCPAdvertisedScopes and MCPCall
- an empty MCP ScopesSupported resolves to the five fixed names including backend
- pier copies advertised scopes and sets MCPCall beside WithDispatch

modules/pier/session.go

@@ -704,7 +704,7 @@ func containsPrompt(prompts []*prompt, name string) bool {
 func (p *Pier) toolHandler(t *tool, session Identity) mcp.ToolHandler {
 	return func(ctx context.Context, req *mcp.CallToolRequest) (*mcp.CallToolResult, error) {
 		id, info := identityFromExtra(req.Extra, session)
-		if req.Session != nil && req.Session.ID() != "" {
+		if !info.stateless && req.Session != nil && req.Session.ID() != "" {
 			info.session = req.Session.ID()
 		}
 		return p.dispatch.call(ctx, id, info, t, req.Params.Arguments), nil