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.App/Services/AgentAdministration.cs

@@ -45,6 +45,17 @@ public sealed class AgentAdministration(AppHost host)
         "SocialMediaManager", "AgentSpawn", "AgentEditor", "Memory", "Taskboard"
     ];
 
+    /// <summary>
+    /// #197: What an agent can be given: the known tools and one per external MCP server — also
+    /// a server's tool an agent still has after the server was removed, so it can be taken away.
+    /// </summary>
+    public IReadOnlyList<string> ToolCatalog()
+        => KnownTools
+            .Concat(host.Instance.McpServers.Select(s => Core.Mcp.McpServerTool.NameFor(s.Id)))
+            .Concat(host.Instance.Agents.SelectMany(a => a.Tools.Keys).Where(k => k.StartsWith(Core.Mcp.McpServerTool.Prefix, StringComparison.OrdinalIgnoreCase)))
+            .Distinct(StringComparer.OrdinalIgnoreCase)
+            .ToList();
+
     public IReadOnlyList<AgentConfig> All => host.Instance.Agents;
 
     public AgentConfig? Find(string agentId)