fix: drop netifaces (unbuildable on runner), harden build install

The packaged exe crashed with ModuleNotFoundError: No module named 'PySide6'.
Root cause: `pip install -e .` aborted because netifaces has no wheel for the
build's Python and needs MSVC to compile from source, so NO dependencies were
installed — and the workflow didn't catch it (native-command failures don't
trip $ErrorActionPreference, and the next pip command succeeded).

- Replace netifaces with a dependency-free socket-based LAN IP detection in the
  GUI; remove netifaces from pyproject and all PyInstaller specs.
- Make pip failures fatal (check $LASTEXITCODE) and add a "Verify runtime
  imports" step that fails the build before bundling if any dep is missing.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

gui/main_window.py

@@ -469,19 +469,39 @@ class MainWindow(QMainWindow):
         # QR/copied URL lets a LAN device authenticate against the API.
         token = self.settings_manager.get_web_auth_token()
         token_qs = f"?token={token}" if token else ""
+        ip = self._detect_lan_ip()
+        if ip:
+            self.ip_label.setText(f"http://{ip}:{DEFAULT_PORT}{token_qs}")
+            return
+        self.ip_label.setText(f"http://localhost:{DEFAULT_PORT}{token_qs}")
+
+    @staticmethod
+    def _detect_lan_ip():
+        """Best-effort primary LAN IPv4, with no third-party dependency.
+
+        Uses a UDP socket to discover which local interface would be used to
+        reach the internet (no packets are actually sent), then falls back to
+        resolving the hostname. Returns None if only loopback is available.
+        """
+        import socket
         try:
-            import netifaces
-            for iface in netifaces.interfaces():
-                addrs = netifaces.ifaddresses(iface)
-                if netifaces.AF_INET in addrs:
-                    for addr in addrs[netifaces.AF_INET]:
-                        ip = addr.get('addr', '')
-                        if ip and not ip.startswith('127.'):
-                            self.ip_label.setText(f"http://{ip}:{DEFAULT_PORT}{token_qs}")
-                            return
+            s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
+            try:
+                s.connect(("8.8.8.8", 80))
+                ip = s.getsockname()[0]
+            finally:
+                s.close()
+            if ip and not ip.startswith("127."):
+                return ip
         except Exception:
             pass
-        self.ip_label.setText(f"http://localhost:{DEFAULT_PORT}{token_qs}")
+        try:
+            for ip in socket.gethostbyname_ex(socket.gethostname())[2]:
+                if not ip.startswith("127."):
+                    return ip
+        except Exception:
+            pass
+        return None
 
     def copy_url_to_clipboard(self):
         """Copy the web interface URL to clipboard."""