fix(ninjitsu): gate Animal Form gump by skill and stop mana drain (#2452) (#2468)

## Issue

Fixes #2452. A player with 30 Ninjitsu reported that the Animal Form menu showed **every** form; selecting one above their skill (e.g. Dog, req 40) **consumed mana** and returned "you need at least 40 skill", and afterwards the **gump never reopened** — every recast silently re-attempted the unusable form and drained more mana.

## Root cause

Three linked bugs, all reproduced from the code:

1. **Gump not gated by skill.** `AnimalFormGump.BuildLayout` compared `Skill.Fixed` (which is `Value * 10`, so 30 skill → `300`) against the raw 0–100 `ReqSkill` (Dog = `40`). `300 >= 40` is always true, so all forms were shown. `Morph` itself correctly uses `.Value`.
2. **Mana charged on a no-skill cast.** `Morph` returns `MorphResult.NoSkill` for an under-skilled form, but both call sites (`OnCast`, `OnResponse`) only special-cased `MorphResult.Fail`; `NoSkill` fell through to the branch that deducts mana.
3. **Menu never reopened.** Per OSI ([uo.com](https://uo.com/wiki/ultima-online-wiki/skills/ninjitsu/), [uoguide](https://www.uoguide.com/Animal_Form)), casting while **standing still always opens the selection menu**, and casting while **moving** quick-transforms into the last selected form. ModernUO only opened the menu when `lastAnimalForm == -1`, so once any form was selected a stationary recast skipped the menu.

## Fix

- Add `AnimalForm.CanSelectEntry` (compares `Skill.Value` to `ReqSkill`, plus the talisman check) and use it for the gump's per-entry enable check.
- `OnCast`: standing still always opens the menu; moving quick-transforms into the last form. `NoSkill` no longer costs mana.
- `OnResponse`: handle `Success` / `Fail` / `NoSkill` explicitly so `NoSkill` costs no mana.

## Tests

Adds `AnimalFormTests`:
- `CanSelectEntry` rejects forms above skill, accepts forms at/below skill, and requires a talisman for talisman-gated forms.
- `Morph` returns `NoSkill` (without transforming) when under-skilled, and `Success` when sufficiently skilled.

Verified the gating test catches the regression (reintroducing `.Fixed` fails it). Full solution build is clean; the 5 new tests plus 284 other UOContent tests pass (the pathfinding/AI sequential tests were excluded only because they deadlock under concurrent local runs — they are unrelated to this change).

Projects/UOContent.Tests/Tests/Spells/Ninjitsu/AnimalFormTests.cs

@@ -0,0 +1,88 @@
+using System;
+using Server.Mobiles;
+using Server.Spells.Ninjitsu;
+using Xunit;
+
+namespace Server.Tests.Spells.Ninjitsu;
+
+[Collection("Sequential UOContent Tests")]
+public class AnimalFormTests
+{
+    private static int IndexOf(Type type) => Array.FindIndex(AnimalForm.Entries, e => e.Type == type);
+
+    private static Mobile NewMobileWithNinjitsu(double skill)
+    {
+        var m = new Mobile(World.NewMobile);
+        m.DefaultMobileInit();
+        m.Skills.Ninjitsu.Base = skill;
+        return m;
+    }
+
+    // Issue #2452: with only 30 Ninjitsu the gump showed every form (including Dog, which needs 40)
+    // because the selectable check compared Skill.Fixed (value x10) against the raw ReqSkill.
+    [Fact]
+    public void CanSelectEntry_FormAboveSkill_IsNotSelectable()
+    {
+        var m = NewMobileWithNinjitsu(30.0);
+
+        Assert.False(AnimalForm.CanSelectEntry(m, AnimalForm.Entries[IndexOf(typeof(Dog))]));  // ReqSkill 40
+        Assert.False(AnimalForm.CanSelectEntry(m, AnimalForm.Entries[IndexOf(typeof(Cat))]));  // ReqSkill 40
+
+        m.Delete();
+    }
+
+    [Fact]
+    public void CanSelectEntry_FormAtOrBelowSkill_IsSelectable()
+    {
+        var m = NewMobileWithNinjitsu(40.0);
+
+        Assert.True(AnimalForm.CanSelectEntry(m, AnimalForm.Entries[IndexOf(typeof(Dog))]));    // ReqSkill 40 (== boundary)
+        Assert.True(AnimalForm.CanSelectEntry(m, AnimalForm.Entries[IndexOf(typeof(Rat))]));    // ReqSkill 20
+        Assert.True(AnimalForm.CanSelectEntry(m, AnimalForm.Entries[IndexOf(typeof(Rabbit))])); // ReqSkill 20
+
+        m.Delete();
+    }
+
+    // Talisman-gated forms are never selectable without the matching talisman, regardless of skill.
+    [Fact]
+    public void CanSelectEntry_TalismanGatedForm_RequiresTalisman()
+    {
+        var m = NewMobileWithNinjitsu(120.0);
+
+        Assert.False(AnimalForm.CanSelectEntry(m, AnimalForm.Entries[IndexOf(typeof(Squirrel))]));
+        Assert.False(AnimalForm.CanSelectEntry(m, AnimalForm.Entries[IndexOf(typeof(Ferret))]));
+
+        m.Delete();
+    }
+
+    // Issue #2452: attempting a form above your skill must report NoSkill (so the caller can
+    // refrain from charging mana) and must not actually transform the caster.
+    [Fact]
+    public void Morph_InsufficientSkill_ReturnsNoSkillAndDoesNotTransform()
+    {
+        var m = NewMobileWithNinjitsu(30.0);
+
+        var result = AnimalForm.Morph(m, IndexOf(typeof(Dog))); // needs 40
+
+        Assert.Equal(AnimalForm.MorphResult.NoSkill, result);
+        Assert.Null(AnimalForm.GetContext(m));
+        Assert.Equal(0, (int)m.BodyMod);
+
+        m.Delete();
+    }
+
+    [Fact]
+    public void Morph_SufficientSkill_TransformsCaster()
+    {
+        // >= ReqSkill + 37.5 guarantees the success-chance roll is skipped.
+        var m = NewMobileWithNinjitsu(60.0);
+
+        var result = AnimalForm.Morph(m, IndexOf(typeof(Rat))); // needs 20
+
+        Assert.Equal(AnimalForm.MorphResult.Success, result);
+        Assert.NotNull(AnimalForm.GetContext(m));
+
+        AnimalForm.RemoveContext(m); // stop the form timer / clear state
+        m.Delete();
+    }
+}