feat: add network access toggle to server settings

Exposes the existing remote server mode through a checkbox in Server
Connection settings. When enabled, the server binds to 0.0.0.0 instead
of 127.0.0.1, making it accessible from other devices on the network.

The plumbing already existed (Rust sidecar passes --host 0.0.0.0 when
remote=true, serverStore has mode state, Python backend accepts --host),
but the UI hardcoded startServer(false). This wires it up.

Closes #104

app/src/App.tsx

@@ -93,10 +93,11 @@ function App() {
     }
 
     serverStartingRef.current = true;
-    console.log('Production mode: Starting bundled server...');
+    const isRemote = useServerStore.getState().mode === 'remote';
+    console.log(`Production mode: Starting bundled server... (remote: ${isRemote})`);
 
     platform.lifecycle
-      .startServer(false)
+      .startServer(isRemote)
       .then((serverUrl) => {
         console.log('Server is ready at:', serverUrl);
         // Update the server URL in the store with the dynamically assigned port