MCP-Client fuer HTTP-Server: externe Werkzeuge durch dieselben Pruefstellen (#197)

- Core/Mcp/McpClient: Streamable HTTP (MCP 2025-06-18) - initialize, tools/list
  with paging, tools/call; answers as JSON or event stream; session kept and
  opened again when the server forgets it; answers capped at 4 MB.
- McpServerTool: one server is one tool (mcp_<id>); its remote tools are the
  operations, so rights, preflight, staging, lead approvals, votes, audit and
  budget apply. On approval by default unless the human trusts an operation;
  reads foreign content; the server's descriptions are cut short and marked.
- McpConnections: registers, refreshes every 15 minutes, follows changes.
- InstanceConfig.mcpServers with protected headers; /api/mcp-servers;
  settings card "External MCP servers"; tool catalog includes the servers.
- stdio servers are not part of this (sandbox runner, separate step).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/ClawdDotNet.Web/Endpoints/ApiEndpoints.cs

@@ -101,7 +101,7 @@ internal static class ApiEndpoints
             var descriptions = host.AgentAdmin.ToolDescriptions();
 
             return host.AgentAdmin.All
-                .Select(a => a.ToDto(descriptions, host.Engine?.IsRunning(a.AgentId) ?? false, host.Tools.Get))
+                .Select(a => a.ToDto(descriptions, host.Engine?.IsRunning(a.AgentId) ?? false, host.Tools.Get, host.AgentAdmin.ToolCatalog()))
                 .ToList();
         });
 
@@ -125,7 +125,8 @@ internal static class ApiEndpoints
                 ? Results.Ok(agent.ToDto(
                     host.AgentAdmin.ToolDescriptions(),
                     host.Engine?.IsRunning(agent.AgentId) ?? false,
-                    host.Tools.Get))
+                    host.Tools.Get,
+                    host.AgentAdmin.ToolCatalog()))
                 : Results.NotFound(new OutcomeDto(false, $"Kein Agent mit der ID '{agentId}'.")));
 
         agents.MapPost("/", (AppHost host, NewAgentDto input) =>