fix(core): DK ToT off-hand strikes and Titan Grip for classless

- Item: 2H weapon subclass/inventory masks for strike spells (ToT / dual 2H).
- Player: allow SPELL_EFFECT_TITAN_GRIP through skill validation; clear TG on
  talent/spec reset only for warriors.
- PlayerStorage: sync m_canTitanGrip from spellbook before inventory load.
- Spell: treat Thassarian off-hand strike spells as OFF_ATTACK when DBC omits
  SPELL_ATTR3_REQUIRES_OFF_HAND_WEAPON.

src/server/game/Spells/Spell.cpp

@@ -61,6 +61,34 @@
 #include "IVMapMgr.h"
 #include "VMapMgr2.h"
 
+namespace
+{
+// Threat of Thassarian off-hand strikes (all ranks). DBC often omits SPELL_ATTR3_REQUIRES_OFF_HAND_WEAPON,
+// so m_attackType would stay BASE_ATTACK and item/damage use the wrong hand (breaks dual 2H / Titan Grip).
+bool IsDKThassarianOffHandStrikeSpell(SpellInfo const* spellInfo)
+{
+    if (!spellInfo || spellInfo->SpellFamilyName != SPELLFAMILY_DEATHKNIGHT || spellInfo->DmgClass != SPELL_DAMAGE_CLASS_MELEE)
+        return false;
+
+    SpellInfo const* first = spellInfo->GetFirstRankSpell();
+    if (!first)
+        return false;
+
+    switch (first->Id)
+    {
+        case 66198: // Obliterate
+        case 66196: // Frost Strike
+        case 66216: // Plague Strike
+        case 66188: // Death Strike
+        case 66217: // Rune Strike
+        case 66215: // Blood Strike
+            return true;
+        default:
+            return false;
+    }
+}
+} // namespace
+
 extern pEffect SpellEffects[TOTAL_SPELL_EFFECTS];
 
 SpellDestination::SpellDestination()
@@ -591,7 +619,7 @@ Spell::Spell(Unit* caster, SpellInfo const* info, TriggerCastFlags triggerFlags,
     switch (m_spellInfo->DmgClass)
     {
         case SPELL_DAMAGE_CLASS_MELEE:
-            if (m_spellInfo->HasAttribute(SPELL_ATTR3_REQUIRES_OFF_HAND_WEAPON))
+            if (m_spellInfo->HasAttribute(SPELL_ATTR3_REQUIRES_OFF_HAND_WEAPON) || IsDKThassarianOffHandStrikeSpell(m_spellInfo))
                 m_attackType = OFF_ATTACK;
             else
                 m_attackType = BASE_ATTACK;