[Bug]: Ensure subnet route CIDRs do not have host bits set

### Description

Tailscale requires that subnet routes use the network address. Update validation logic in frontend and backend to verify that host bits are not set.

Ref: tailscale/tailscale#18243

### Plugin Version

N/A

### Unraid Version

N/A

### Steps To Reproduce

_No response_

### Anything else?

_No response_