web-wallet: Detect network connection

[kieranhall]

The web-wallet needs to behave similar to the explorer, in that it needs to determine the network URL to use when interfacing with a node. Currently the wallet it passed VITE_LOCAL_NODE, which needs to be eliminated. Instead the wallet will need to default to using it's own host (assuming that it's a locally hosted app).

The wallet should only use a specific node URL if one is passed via VITE_NODE_URL (to be consistent with the explorer app.