Add exit node support to the wasm JS bridge:
- Include `exitNodeOption` and `stableNodeID` on each peer in the
notifyNetMap payload so callers can identify which peers are exit
nodes and reference them by stable ID.
- Call `notifyExitNode(stableNodeID)` whenever prefs change, so
callers can track which exit node (if any) is currently active.
- Expose `setExitNode(stableNodeID)` — sets ExitNodeID via EditPrefs.
- Expose `setExitNodeEnabled(enabled)` — toggles the last-used exit
node on/off via SetUseExitNodeEnabled.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>