feat(multiplayer): wire ranked profile runtime policy

server/domain/rating.go

@@ -87,6 +87,19 @@ type TierPolicy struct {
 	bands []TierBand
 }
 
+// DefaultTierPolicy is the backend-owned launch policy used by runnable API
+// binaries. Callers still serialize only the resulting tier; clients never
+// receive or reproduce these thresholds.
+func DefaultTierPolicy() TierPolicy {
+	return TierPolicy{bands: []TierBand{
+		{Tier: RankTierBronze, MinRating: 0},
+		{Tier: RankTierSilver, MinRating: 1200},
+		{Tier: RankTierGold, MinRating: 1500},
+		{Tier: RankTierPlatinum, MinRating: 1800},
+		{Tier: RankTierDiamond, MinRating: 2200},
+	}}
+}
+
 func NewTierPolicy(bands []TierBand) (TierPolicy, error) {
 	if len(bands) == 0 || bands[0].MinRating > 0 {
 		return TierPolicy{}, fmt.Errorf("tier policy must start at or below zero")