mobile: fullscreen (immersive Android + PWA) + auto-hide reported nudity avatars

Fullscreen on mobile:
- Android (Capacitor): MainActivity now runs edge-to-edge and hides the status +
  navigation bars (immersive, transient-on-swipe), re-asserted on focus.
- PWA: manifest display -> "fullscreen" with display_override fallback chain;
  viewport gains viewport-fit: cover for proper safe-area/edge-to-edge handling.

Moderation auto-hide:
- ProfileService.ReportUser now de-dupes nudity reports per reporter and, once
  NudityHideThreshold (3) distinct players flag a target's avatar as nudity,
  auto-removes their custom photo (reverts to default avatar). Counted from the
  ledger, so still no schema change.

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

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

@@ -54,19 +54,52 @@ public class ProfileService
         await _db.SaveChangesAsync();
     }
 
+    /// <summary>Distinct players who must flag an avatar as nudity before it auto-hides.</summary>
+    public const int NudityHideThreshold = 3;
+
     /// <summary>
     /// Record a moderation report (inappropriate avatar / insulting chat). Stored
     /// in the write-only ledger as kind="report" so no schema change is needed;
-    /// Ref encodes "{targetId}|{reason}|{details}".
+    /// Ref encodes "{targetId}|{reason}|{details}". Once enough *distinct* players
+    /// flag a target's avatar as nudity, the custom photo is auto-removed.
     /// </summary>
     public async Task ReportUser(string reporterUid, string targetId, string? reason, string? details)
     {
-        if (string.IsNullOrWhiteSpace(targetId)) return;
+        if (string.IsNullOrWhiteSpace(targetId) || targetId == reporterUid) return;
         var safeReason = reason is "nudity" or "insult" or "other" ? reason : "other";
         var safeDetails = (details ?? "").Replace("\n", " ").Trim();
         var @ref = $"{targetId}|{safeReason}|{safeDetails}";
         if (@ref.Length > 480) @ref = @ref[..480];
+
+        var nudityPrefix = targetId + "|nudity";
+        // De-dupe nudity reports so a single player can't nuke an avatar alone.
+        if (safeReason == "nudity")
+        {
+            var already = await _db.Ledger.AnyAsync(
+                l => l.Kind == "report" && l.UserId == reporterUid && l.Ref!.StartsWith(nudityPrefix));
+            if (already) return;
+        }
+
         await Ledger(reporterUid, "report", 0, @ref);
+
+        // Auto-hide a custom avatar once enough distinct players flag it.
+        if (safeReason == "nudity")
+        {
+            var reporters = await _db.Ledger
+                .Where(l => l.Kind == "report" && l.Ref!.StartsWith(nudityPrefix))
+                .Select(l => l.UserId)
+                .Distinct()
+                .CountAsync();
+            if (reporters >= NudityHideThreshold)
+            {
+                var target = await GetOrCreate(targetId, null);
+                if (!string.IsNullOrEmpty(target.AvatarImage))
+                {
+                    target.AvatarImage = null; // revert to their default avatar
+                    await SaveInternal(target);
+                }
+            }
+        }
     }
 
     public async Task<ProfileDto> Update(string uid, JsonElement patch)