balance(achievements): strictly-escalating milestone coin rewards

The old reward formula rounded (40+6g)/50 on the raw goal, so adjacent
milestones could pay the same (e.g. "1 win" and "5 wins" both 50) and the curve
was lumpy — not a standard escalating-reward ladder. Reward now scales by tier
index: 50, 150, 250 … capped at 1500, strictly increasing per milestone.
Mirrored client (gamification.ts) + server (Gamification.cs) so live grants match.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

server/src/Hokm.Server/Profiles/Gamification.cs

@@ -56,12 +56,13 @@ public static class Gamification
     // metric: wins|kotsFor|bestWinStreak|shutoutWins|games|tricks|level ; ratingFloor>0 = rank ach.
     private record AchDef(string Id, string? Metric, int RatingFloor, int Goal, int Coin, string NameFa, string NameEn, string Icon);
     // Mirrors src/lib/online/gamification.ts (same ids/goals/coins/metrics).
-    private static int Coin(int g) => Math.Min(1500, Math.Max(50, (int)Math.Floor((40.0 + g * 6) / 50.0 + 0.5) * 50));
+    // Reward escalates strictly per milestone tier (50, 150, 250 … capped 1500).
+    private static int CoinAt(int i) => Math.Min(1500, 50 + i * 100);
     private static string Fa(int n) =>
         new string(n.ToString().Select(c => c is >= '0' and <= '9' ? "۰۱۲۳۴۵۶۷۸۹"[c - '0'] : c).ToArray());
 
     private static AchDef[] Tier(string metric, string prefix, string icon, int[] goals, Func<int, string> faName, Func<int, string> enName)
-        => goals.Select(g => new AchDef($"{prefix}_{g}", metric, 0, g, Coin(g), faName(g), enName(g), icon)).ToArray();
+        => goals.Select((g, i) => new AchDef($"{prefix}_{g}", metric, 0, g, CoinAt(i), faName(g), enName(g), icon)).ToArray();
 
     private static readonly AchDef[] Achs = BuildAchs();
     private static AchDef[] BuildAchs()

src/lib/online/gamification.ts

@@ -253,12 +253,13 @@ function tier(
   faDesc: (g: string) => string,
   enDesc: (g: number) => string
 ): AchievementDef[] {
-  return goals.map((g) => ({
+  return goals.map((g, i) => ({
     id: `${prefix}_${g}`,
     category,
     metric,
     goal: g,
-    coinReward: Math.min(1500, Math.max(50, Math.round((40 + g * 6) / 50) * 50)),
+    // Reward escalates strictly per milestone tier (50, 150, 250 … capped 1500).
+    coinReward: Math.min(1500, 50 + i * 100),
     icon,
     nameFa: faName(faNum(g)),
     nameEn: enName(g),