Fix web GUI crash: detect LAN IP for WebSocket public_url

public_url="" caused IndexError in textual-serve URL builder.
Now auto-detects the machine's LAN IP when binding to 0.0.0.0
so the browser can connect to the correct WebSocket endpoint.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tui/__main__.py

@@ -1,4 +1,5 @@
 import os
+import socket
 import sys
 from pathlib import Path
 
@@ -8,24 +9,43 @@ from tui.app import GnizaApp
 _ROOT = os.environ.get("GNIZA_DIR", str(Path(__file__).resolve().parent.parent))
 
 
+def _get_local_ip() -> str:
+    """Get the machine's LAN IP for public_url."""
+    try:
+        s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
+        s.connect(("8.8.8.8", 80))
+        ip = s.getsockname()[0]
+        s.close()
+        return ip
+    except Exception:
+        return "localhost"
+
+
 def main():
     if "--web" in sys.argv:
         from textual_serve.server import Server
         port = 8080
         host = "0.0.0.0"
+        public_host = None
         for i, arg in enumerate(sys.argv):
             if arg == "--port" and i + 1 < len(sys.argv):
                 port = int(sys.argv[i + 1])
             elif arg == "--host" and i + 1 < len(sys.argv):
                 host = sys.argv[i + 1]
+                public_host = host
         os.environ["PYTHONPATH"] = f"{_ROOT}:{os.environ.get('PYTHONPATH', '')}"
         os.environ["GNIZA_DIR"] = _ROOT
+        # textual-serve uses public_url to build WebSocket URLs.
+        # If binding to 0.0.0.0, detect the real IP for the browser.
+        if public_host is None:
+            public_host = _get_local_ip() if host == "0.0.0.0" else host
+        public_url = f"http://{public_host}:{port}"
         server = Server(
             "python3 -m tui",
             host=host,
             port=port,
             title="gniza",
-            public_url="",
+            public_url=public_url,
         )
         server.serve()
     else: