chore: cleanup possession handling (#1984)

* feat: enhance possession mechanics with skill set integration and improved message handling

* fix: restore SetPossessor in Mount() and scope IsRacing to vehicles

SetPossessor was missing from Mount(), breaking direct possessions via
PossessableComponent::OnUse which bypasses HandlePossession. IsRacing
now only set/cleared when the mount has HavokVehiclePhysicsComponent,
preventing non-vehicle possessions from incorrectly affecting the
distance-driven statistic.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

dGame/dComponents/PossessableComponent.h

@@ -55,6 +55,12 @@ public:
 	 */
 	bool GetDepossessOnHit() const { return m_DepossessOnHit; };
 
+	/**
+	 * Returns the skill set ID for this possessable (0 = no skill set)
+	 * @return the skill set ID
+	 */
+	int32_t GetSkillSet() const { return m_SkillSet; };
+
 	/**
 	 * Forcibly depossess the Entity
 	 */
@@ -118,4 +124,9 @@ private:
 	 *
 	 */
 	bool m_ItemSpawned = false;
+
+	/**
+	 * @brief Skill set ID from PossessableComponent CDClient table (0 = none)
+	 */
+	int32_t m_SkillSet = 0;
 };