feat(doctor): surface xAI model retirement in hermes doctor

Add a new section in run_doctor that lists retired xAI model
references found in the active config and points the user at the
official xAI migration guide.

Each retired reference shows its config path (principal.model,
auxiliary.<slot>.model, delegation.model, tts.xai.model, or
plugins.image_gen.xai.model), the recommended replacement, and
whether reasoning_effort needs to be set (for non-reasoning variants
that map to grok-4.3 + reasoning_effort=none).

Findings are appended to manual_issues so the final doctor summary
reminds the user to update their config.yaml manually (no automatic
YAML rewriting in this PR — preserves comments, key order, types).

Wrapped in try/except so doctor still completes if load_config or
the retirement module raise unexpectedly.

hermes_cli/doctor.py

@@ -777,7 +777,33 @@ def run_doctor(args):
         except Exception:
             pass
 
+    _section("xAI Model Retirement (May 15, 2026)")
+
+    try:
+        from hermes_cli.config import load_config
+        from hermes_cli.xai_retirement import (
+            MIGRATION_GUIDE_URL,
+            find_retired_xai_refs,
+            format_issue,
+        )
+
+        _xai_cfg = load_config()
+        retired_refs = find_retired_xai_refs(_xai_cfg)
+        if not retired_refs:
+            check_ok("No retired xAI models in config")
+        else:
+            for ref in retired_refs:
+                check_warn(format_issue(ref))
+            check_info(f"Migration guide: {MIGRATION_GUIDE_URL}")
+            manual_issues.append(
+                f"Update {len(retired_refs)} retired xAI model reference(s) "
+                f"in config.yaml — see {MIGRATION_GUIDE_URL}"
+            )
+    except Exception as _xai_check_err:
+        check_warn("xAI retirement check skipped", f"({_xai_check_err})")
+
     _section("Auth Providers")
+
     try:
         from hermes_cli.auth import (
             get_nous_auth_status,