fix(feature-flags): define stock flag defaults in code so JSONs exist on first boot (#2653)

### Summary

`default-flags.json` was never shipped — `Configuration/` is gitignored — so the predefined-flag loader has been dead since #2328. A fresh shard boots with 0 flags and writes no JSON until an admin changes something, so `[FeatureList` is empty on first run.

Stock flags are now defined in code. `Initialize()` runs `Load()` first, then `LoadDefaultFlags()` seeds any of the 14 stock keys the save is missing, reading each default from the static it syncs (`ServerFeatureFlags` / `ContentFeatureFlags`) rather than a duplicated boolean — so `speedhack_detection` stays off and `insurance` honors `Insurance.Configure` (`insurance.enable`). Existing entries are never overwritten, so admin state survives upgrades and saves predating a flag pick it up. `Save()` runs only when something was seeded, so all five JSON files exist from first boot.

Verified: `dotnet build Projects/UOContent/UOContent.csproj -c Release`, 0 warnings 0 errors.

Projects/UOContent/Engines/FeatureFlags/FeatureFlagManager.cs

@@ -40,9 +40,8 @@ public static class FeatureFlagManager
             Directory.CreateDirectory(savePath);
         }
 
-        // Load predefined flags from JSON, then overlay runtime state
-        LoadDefaultFlags();
         Load();
+        LoadDefaultFlags();
 
         _initialized = true;
         logger.Information(
@@ -751,14 +750,55 @@ public static class FeatureFlagManager
 
     private static void LoadDefaultFlags()
     {
-        var defaultFlagsPath = Path.Combine(Core.BaseDirectory, "Configuration", "FeatureFlags", "default-flags.json");
+        (string Key, string Category, string Description, bool Enabled)[] defaults =
-        var defaultFlags = JsonConfig.Deserialize<List<FeatureFlag>>(defaultFlagsPath);
+        [
-        if (defaultFlags != null)
+            ("player_trading", "Economy", "Allow secure trades between players", ServerFeatureFlags.PlayerTrading),
+            ("pvp_combat", "Combat", "Allow player vs player combat", ServerFeatureFlags.PvPCombat),
+            ("bank_access", "Economy", "Allow players to access their bank boxes", ServerFeatureFlags.BankAccess),
+            ("speedhack_detection", "System", "Enable speedhack detection", ServerFeatureFlags.SpeedhackDetection),
+            ("insurance", "Economy", "Enable item insurance", ServerFeatureFlags.InsuranceEnabled),
+            ("vendor_purchase", "Economy", "Allow purchasing from NPC vendors", ContentFeatureFlags.VendorPurchase),
+            ("vendor_sell", "Economy", "Allow selling to NPC vendors", ContentFeatureFlags.VendorSell),
+            ("player_vendors", "Economy", "Allow player vendor interactions", ContentFeatureFlags.PlayerVendors),
+            ("house_placement", "Housing", "Allow new house placements", ContentFeatureFlags.HousePlacement),
+            ("boat_placement", "Housing", "Allow new boat placements", ContentFeatureFlags.BoatPlacement),
+            ("bulk_orders", "Crafting", "Allow bulk order deeds", ContentFeatureFlags.BulkOrders),
+            ("passive_detect_hidden", "System", "Enable passive detect hidden", ContentFeatureFlags.PassiveDetectHidden),
+            ("young_player_system", "System", "Enable the young player system", ContentFeatureFlags.YoungPlayerSystem),
+            ("bitmap_pathfinding_cache", "Performance", "Enable the bitmap pathfinding cache", ContentFeatureFlags.BitmapPathfindingCache),
+        ];
+
+        var now = Core.Now;
+        var added = 0;
+
+        for (var i = 0; i < defaults.Length; i++)
         {
-            foreach (var flag in defaultFlags)
+            var (key, category, description, enabled) = defaults[i];
+            if (_flags.ContainsKey(key))
             {
-                _flags.TryAdd(flag.Key, flag);
+                continue;
             }
+
+            _flags.Add(
+                key,
+                new FeatureFlag
+                {
+                    Key = key,
+                    Description = description,
+                    Category = category,
+                    DefaultEnabled = enabled,
+                    Enabled = enabled,
+                    LastModified = now,
+                    LastModifiedBy = "System"
+                }
+            );
+            added++;
+        }
+
+        if (added > 0)
+        {
+            Save();
+            logger.Information("Seeded {Count} default feature flag(s)", added);
         }
     }