debug(combat): explicit error catch + null-check logging

If the CombatStatsTracker constructor throws (e.g. TypeInitializationException
from static field initializers), we now catch and print the exact exception
type + message + inner exception to the DECAL chat window.

Also logs "tracker=OK" or "tracker=NULL" in LoginComplete so we can see
if the object was created at all.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

MosswartMassacre/PluginCore.cs

@@ -349,7 +349,16 @@ namespace MosswartMassacre
                 _vitalSharingTracker = new VitalSharingTracker(this);
 
                 // Initialize combat stats tracker (Mag-Tools style combat parsing)
-                _combatStatsTracker = new CombatStatsTracker(this);
+                try
+                {
+                    _combatStatsTracker = new CombatStatsTracker(this);
+                }
+                catch (Exception combatEx)
+                {
+                    WriteToChat($"[CombatStats] FATAL: Failed to create tracker: {combatEx.GetType().Name}: {combatEx.Message}");
+                    if (combatEx.InnerException != null)
+                        WriteToChat($"[CombatStats] Inner: {combatEx.InnerException.GetType().Name}: {combatEx.InnerException.Message}");
+                }
 
                 // Initialize command router
                 _commandRouter = new CommandRouter();
@@ -547,6 +556,7 @@ namespace MosswartMassacre
             _staticRareTracker = _rareTracker;
             _chatEventRouter.SetRareTracker(_rareTracker);
             _chatEventRouter.SetCombatTracker(_combatStatsTracker);
+            WriteToChat($"[CombatStats] tracker={(_combatStatsTracker != null ? "OK" : "NULL")}");
 
             // Apply the values
             _rareTracker.RareMetaEnabled = PluginSettings.Instance.RareMetaEnabled;