refactor: consolidate network interface detection logic

Move platform-specific network interface detection from cmd/cli/ to root package
as ValidInterfaces function. This eliminates code duplication and provides a
consistent interface for determining valid physical network interfaces across
all platforms.

- Remove duplicate validInterfacesMap functions from platform-specific files
- Add context parameter to virtualInterfaces for proper logging
- Update all callers to use ctrld.ValidInterfaces instead of local functions
- Improve error handling in virtual interface detection on Linux

cmd/cli/net_windows.go

@@ -1,10 +1,7 @@
 package cli
 
 import (
-	"context"
 	"net"
-
-	"github.com/Control-D-Inc/ctrld"
 )
 
 func patchNetIfaceName(iface *net.Interface) (bool, error) {
@@ -17,12 +14,3 @@ func validInterface(iface *net.Interface, validIfacesMap map[string]struct{}) bo
 	_, ok := validIfacesMap[iface.Name]
 	return ok
 }
-
-// validInterfacesMap returns a set of all physical interfaces.
-func validInterfacesMap(ctx context.Context) map[string]struct{} {
-	m := make(map[string]struct{})
-	for ifaceName := range ctrld.ValidInterfaces(ctx) {
-		m[ifaceName] = struct{}{}
-	}
-	return m
-}