fix(telegram): address review findings

- A speech or download timeout (TaskCanceledException nobody asked for) is a failure
  with the user notice, not a silent shutdown; OpenAiSpeechToText maps it to
  "the request timed out."; UpdateRouter only treats the caller's cancellation as shutdown.
- send: WorkspacePaths resolves the real path component by component (realpath),
  closing the directory-link-inside-target bypass; `.` reports a directory.
- Image documents are attached inline only when their magic bytes are JPEG/PNG/GIF/WebP,
  under the detected type.
- Audio goes to STT as an ASCII audio.<ext> name.
- MCP Browser section mentions send only when it is active.
- RunInOrderAsync takes a cancellation token; queued work is skipped once disposal gives up;
  SendReplyAsync stays private behind ReplyInOrderAsync.
- Speech HttpClient handler recycles pooled connections; BuiltInTools.Send();
  IExtensionHost.Channel is abstract; WorkspacePaths in its own file.
- Tests: timeouts, symlink chains (Linux), sniffing, channel delivery failures,
  queued-work cancellation, gated voice ordering. Spec and docs updated.

extensions/Volcanic.AgenticCore.Extensions.Mcp/McpExtension.cs

@@ -129,7 +129,7 @@ public sealed class McpExtension : IExtension
     private void AddPromptSections(IExtensionApi api, SystemPromptOptions options)
     {
         var active = api.GetActiveTools().ToHashSet(StringComparer.Ordinal);
-        var hasSend = api.GetAllTools().Any(t => t.Name == "send");
+        var hasSend = active.Contains("send"); // registered but inactive: the model can't call it
         foreach (var server in _servers)
         {
             if (!server.RegisteredTools.Any(active.Contains)) continue;