Add warning when port forwards are used in bridged/shared mode

[mstrofnone]

Changes

This PR adds an inline warning note in the network configuration view that appears when the user selects 'Bridged' or 'Shared' network mode.

Problem

UTM's UI lets users add PortForward entries to a Bridged or Shared network adapter, but those forwards are silently ignored by the QEMU command-line generator because Apple's vmnet framework doesn't support hostfwd=. Users discover this empirically — port forwards just don't work, no warning given.

Solution

Added a note (in orange, using the footnote font) that appears only when network mode is Bridged or Shared, stating that port forwards are only honored in Emulated mode due to vmnet framework limitations.

The change is in Platform/Shared/VMConfigNetworkView.swift and only affects macOS (wrapped in #if os(macOS)).

Testing

• Open UTM on macOS
• Create or edit a VM's network configuration
• Select 'Bridged (Advanced)' or 'Shared Network' mode
• Observe the orange note appearing below the network mode selection
• Port forwards UI should still be visible (for user's reference if they switch modes)