fix: resolve Electron startup failures on Windows and Linux

- Try legacy port (61337) first to preserve existing users' localStorage,
  fall back to 13370 which is below the Windows Hyper-V ephemeral range (#705)
- Bind server and all URL references to 127.0.0.1 instead of localhost
  to fix IPv4/IPv6 mismatch on Linux (#684)
- Add OS-assigned port fallback (port 0) so startup never throws
- Log error codes in port checks for easier debugging
- Update localhost guards in index.ts and window-manager.ts to also
  match 127.0.0.1

Related: #705, #684

electron/main/next-server.ts

@@ -68,7 +68,7 @@ export async function startNextServer(): Promise<string> {
     const env: Record<string, string> = {
         NODE_ENV: "production",
         PORT: String(port),
-        HOSTNAME: "localhost",
+        HOSTNAME: "127.0.0.1",
         // Enable Node.js built-in proxy support for fetch (Node.js 24+)
         NODE_USE_ENV_PROXY: "1",
     }