fix(dashboard): skip browser-open on headless Linux to prevent process exit

Fixes #24127

On headless Linux VPS (no DISPLAY or WAYLAND_DISPLAY), some Python
webbrowser backends register TUI programs such as links, lynx, or
www-browser.  GenericBrowser.open() spawns these without redirecting
stdin/stdout, allowing them to take over the terminal.  This can cause
the process to receive SIGHUP and exit immediately even though uvicorn
bound the port successfully, producing a misleading success message
followed by an empty --status.

Fix: detect headless Linux at startup and skip the auto-open when no
display server is available.  On such systems the URL is still printed
so the user can open it manually or via an SSH tunnel.  The webbrowser
call is also wrapped in a try/except so any unexpected failure on other
platforms is silently absorbed rather than surfacing as an unhandled
exception in the daemon thread.

hermes_cli/web_server.py

@@ -4432,11 +4432,33 @@ def start_server(
     if open_browser:
         import webbrowser
 
-        def _open():
-            time.sleep(1.0)
-            webbrowser.open(f"http://{host}:{port}")
+        # On headless Linux (no DISPLAY or WAYLAND_DISPLAY) some registered
+        # browsers are TUI programs (links, lynx, www-browser) that try to
+        # take over the terminal.  That can send SIGHUP to the server process
+        # and cause an immediate exit even though uvicorn bound successfully.
+        # Skip the auto-open attempt on headless systems and let the user
+        # open the URL manually.  macOS and Windows are always considered
+        # display-capable.
+        _has_display = (
+            sys.platform != "linux"
+            or bool(os.environ.get("DISPLAY"))
+            or bool(os.environ.get("WAYLAND_DISPLAY"))
+        )
 
-        threading.Thread(target=_open, daemon=True).start()
+        if _has_display:
+            def _open():
+                try:
+                    time.sleep(1.0)
+                    webbrowser.open(f"http://{host}:{port}")
+                except Exception:
+                    pass
+
+            threading.Thread(target=_open, daemon=True).start()
+        else:
+            _log.debug(
+                "Skipping browser-open: no DISPLAY or WAYLAND_DISPLAY detected "
+                "(headless Linux). Pass --no-open to suppress this detection."
+            )
 
     print(f"  Hermes Web UI → http://{host}:{port}")
     uvicorn.run(app, host=host, port=port, log_level="warning")