fix: Streamlines insurance. Insurance only executes when enabled. (#2550)

### Summary

Moves inventory insurance out of `Mobile`/`PlayerMobile` into its own system at `Projects/UOContent/Engines/Insurance/`, wires it into the feature flag system, and makes disabling it actually disable it everywhere.

### Changes

**New `Server.Engines.Insurance.Insurance` system**

* Owns its own `Configure()`, seeding from the existing `insurance.enable` setting (default `Core.AOS`), so no config migration is needed. `Mobile.InsuranceEnabled` is gone, along with its line in `ExpansionConfiguration`.
* `CanInsure`, `GetInsuranceCost`, `ToggleItemInsurance`, `AutoRenewInventoryInsurance`, `CancelRenewInventoryInsurance` and `OpenItemInsuranceMenu` move here from `PlayerMobile`, which keeps four one-line shims for the context-menu callbacks.
* Every entry point is gated on `Insurance.Enabled`, and the death-time state is only allocated when insurance is on — a shard without insurance pays nothing for it.

**Feature flag integration**

Insurance is now a first-class feature flag: `ServerFeatureFlags.InsuranceEnabled`, registered under the `insurance` key in `FeatureFlagManager.SyncStaticFlag`, so it can be inspected and toggled through the normal flag command/gump rather than only at boot. `Insurance.Enabled` reads through to the flag, so there is one source of truth for every consumer.

**Fixes a memory leak from PvP**

`PlayerMobile.m_InsuranceAward` was a `Mobile` field assigned on every death and never cleared, so every player permanently pinned a strong reference to the last player who killed them. Killers were kept alive by their victims indefinitely.

Death-time insurance state now lives in a `Dictionary<Mobile, InsuranceContext>` owned by the insurance system: the entry is created in `OnBeforeDeath` and removed in `OnDeath`, so nothing outlives the death that created it.

**Removes insurance fields from every PlayerMobile**

`m_InsuranceAward`, `m_InsuranceBonus` and `m_NonAutoreinsuredItems` were carried by every `PlayerMobile` whether or not the shard ran insurance. All three are gone; the equivalent state is allocated per-death, only for players who actually die with insured items, only when insurance is enabled.

**Stale `Insured` flags are inert when insurance is off**

`Item.Insured` is a persisted flag, so items stay marked after a shard turns insurance off. Every read path now checks the flag first, so those items behave exactly as if they were never insured:

* `Item.CheckBlessed` / `Item.IsStandardLoot` — they drop again instead of acting blessed
* `Item.AddLootTypeProperty` — no more phantom "insured" tooltip
* `PlayerMobile.FindItems_Callback` — not yanked out of nested bags on death
* `DestroyEquipment` — no longer immune
* `ClothingBlessDeed` — no longer reports "that item is already blessed"

**Gumps promoted out of `PlayerMobile`**

`ItemInsuranceMenuGump`, `ItemInsuranceMenuConfirmGump` and `CancelRenewInventoryInsuranceGump` were private nested classes reaching into `PlayerMobile` privates. They are now public types in `Engines/Insurance/Gumps/`, talking to the insurance system through its public API. `ItemInsuranceMenuGump.ToggleSelected()` replaces the confirm gump's reach-in to the parent's `_items`/`_insure` arrays.

### Behavior changes

* The per-item "You lack the funds to purchase the insurance" message on failed auto-renewal is no longer sent during death; players get the single 1061115 summary instead. Marked with a TODO pending a decision on whether the per-item message should spam.
* The killer's insurance bonus is deposited once at the end of death processing rather than 300 gold at a time per insured item, and the "gold has been deposited" message is now conditional on the deposit succeeding. Same total.

### Drive-by cleanups

`PoisonImpl.IncreaseLevel` -> `Poison.IncreaseLevel`, a redundant `is NetState { } ns` pattern, `new List<Item>(Items)` -> collection expression, alignment of the `SyncStaticFlag` switch arms, and some comment/formatting fixes in `PlayerMobile`.

Projects/Server/FeatureFlags.cs

@@ -10,4 +10,5 @@ public static class ServerFeatureFlags
     public static bool PvPCombat { get; set; } = true;
     public static bool BankAccess { get; set; } = true;
     public static bool SpeedhackDetection { get; set; }
+    public static bool InsuranceEnabled { get; set; }
 }

Projects/Server/Items/Item.cs

@@ -1884,7 +1884,7 @@ public partial class Item : IHued, IComparable<Item>, ISpawnable, IObjectPropert
         {
             list.Add(1049643); // cursed
         }
-        else if (Insured)
+        else if (ServerFeatureFlags.InsuranceEnabled && Insured)
         {
             list.Add(1061682); // <b>insured</b>
         }
@@ -4216,12 +4216,12 @@ public partial class Item : IHued, IComparable<Item>, ISpawnable, IObjectPropert
     }
 
     public virtual bool CheckBlessed(Mobile m) =>
-        m_LootType == LootType.Blessed || Mobile.InsuranceEnabled && Insured || m != null && m == BlessedFor;
+        m_LootType == LootType.Blessed || ServerFeatureFlags.InsuranceEnabled && Insured || m != null && m == BlessedFor;
 
     public virtual bool CheckNewbied() => m_LootType == LootType.Newbied;
 
     public virtual bool IsStandardLoot() =>
-        (!Mobile.InsuranceEnabled || !Insured) && BlessedFor == null && m_LootType == LootType.Regular;
+        (!ServerFeatureFlags.InsuranceEnabled || !Insured) && BlessedFor == null && m_LootType == LootType.Regular;
 
     public override string ToString() => $"{Serial} \"{GetType().Name}\"";
 

Projects/Server/Mobiles/Mobile.cs

@@ -953,8 +953,6 @@ public partial class Mobile : IHued, IComparable<Mobile>, ISpawnable, IObjectPro
 
     public static TimeSpan AutoManifestTimeout { get; set; } = TimeSpan.FromSeconds(5.0);
 
-    public static bool InsuranceEnabled { get; set; }
-
     public static int ActionDelay { get; set; } = 500;
 
     public static VisibleDamageType VisibleDamageType { get; set; }