fix(auth): don't launch a text-mode browser inside the terminal for OAuth (#34479)

OAuth auto-open only checked _is_remote_session() (SSH + cloud-shell env
vars). On a headless/CLI-only Linux box with no GUI browser, none of those
trip, so webbrowser.open() resolved to a console browser (w3m/lynx/links)
and launched it INSIDE the terminal — hijacking the user's TTY with the
xAI 'Account Management' login page instead of letting them copy the URL.

Add _can_open_graphical_browser(): returns False when webbrowser would
resolve to a known console browser, when $BROWSER names one, when there's
no display server on Linux, or when no browser resolves at all. Gate all 5
OAuth auto-open callsites (xAI loopback, Spotify loopback, MiniMax device
code, Anthropic, Google) on it in addition to the existing remote check.
Headless boxes now print the URL / fall through to manual-paste instead.

agent/anthropic_adapter.py

@@ -1256,10 +1256,16 @@ def run_hermes_oauth_login_pure() -> Optional[Dict[str, Any]]:
     print()
 
     try:
-        webbrowser.open(auth_url)
-        print("  (Browser opened automatically)")
+        from hermes_cli.auth import _can_open_graphical_browser as _can_open_gui
     except Exception:
-        pass
+        _can_open_gui = lambda: True  # noqa: E731 — degrade to prior behavior
+
+    if _can_open_gui():
+        try:
+            webbrowser.open(auth_url)
+            print("  (Browser opened automatically)")
+        except Exception:
+            pass
 
     print()
     print("After authorizing, you'll see a code. Paste it below.")

agent/google_oauth.py

@@ -899,7 +899,15 @@ def start_oauth_flow(
         try:
             import webbrowser
 
-            webbrowser.open(auth_url, new=1, autoraise=True)
+            try:
+                from hermes_cli.auth import (
+                    _can_open_graphical_browser as _can_open_gui,
+                )
+            except Exception:
+                _can_open_gui = lambda: True  # noqa: E731
+
+            if _can_open_gui():
+                webbrowser.open(auth_url, new=1, autoraise=True)
         except Exception as exc:
             logger.debug("webbrowser.open failed: %s", exc)