Add core modules (SSH args parser, cache, resolver, NetBox client) with tests

internal/resolver/primary_ip.go

@@ -0,0 +1,23 @@
+package resolver
+
+import (
+	"context"
+
+	"git.zb-server.de/Sebi/ssh-netbox-wrapper/internal/netbox"
+)
+
+// PrimaryIPStrategy returns the primary IP configured in NetBox.
+// Prefers IPv4, falls back to IPv6.
+type PrimaryIPStrategy struct{}
+
+func (s *PrimaryIPStrategy) Name() string { return "primary_ip" }
+
+func (s *PrimaryIPStrategy) Resolve(_ context.Context, entry *netbox.HostEntry, _ *netbox.Client) (string, error) {
+	if entry.PrimaryIP4 != "" {
+		return entry.PrimaryIP4, nil
+	}
+	if entry.PrimaryIP6 != "" {
+		return entry.PrimaryIP6, nil
+	}
+	return "", ErrNoIP
+}