docs(comments): trim verbose dispose and thread rationale

Match the new HellionChat comment-length convention: 1-3 lines for
standard pitfall notes, 5+ only for non-trivial workarounds. The
previous Dispose comment was 14 lines of textbook prose, which veered
into AI-slop territory and would rot on the next refactor.

HellionChat/MessageManager.cs

@@ -66,11 +66,8 @@ internal class MessageManager : IAsyncDisposable
 
         Store = new MessageStore(DatabasePath());
 
-        // IsBackground = true so a stuck worker never blocks plugin unload.
-        // The worker has its own cancellation path via PendingThreadCancellationToken,
-        // and DisposeAsync waits up to 10s for cooperative shutdown. The
-        // background flag is the safety net for the case where cooperative
-        // shutdown fails to drain the queue in time.
+        // IsBackground so a stuck worker never blocks plugin unload.
+        // Cooperative cancel via PendingThreadCancellationToken first, background flag is the safety net.
         PendingMessageThread = new Thread(() => ProcessPendingMessages(PendingThreadCancellationToken.Token))
         {
             IsBackground = true,

HellionChat/MessageStore.cs

@@ -131,20 +131,10 @@ internal class MessageStore : IDisposable
 
     public void Dispose()
     {
-        // Order matters: Close releases the WAL/SHM files, Dispose then
-        // hands the underlying connection state back to the pool. We
-        // intentionally configure Pooling = false in Connect(), so there
-        // is no pool to clear globally, which keeps HellionChat's reload
-        // from disturbing other plugins' SQLite connections (which is
-        // what SqliteConnection.ClearAllPools() would do, since it acts
-        // provider-wide).
-        //
-        // We used to call GC.Collect() + GC.WaitForPendingFinalizers()
-        // here as a defensive flush, but with Pooling = false there is
-        // nothing left to collect that the explicit Close hasn't already
-        // released. The GC calls were heap pressure on every plugin
-        // reload and reached into other plugins' object graphs because
-        // GC.Collect is process-wide.
+        // Pooling=false (set in Connect) avoids ClearAllPools, which is
+        // provider-wide and would touch other plugins' SQLite connections.
+        // GC.Collect was here as a defensive flush; removed because explicit
+        // Close already releases everything we hold.
         Connection.Close();
         Connection.Dispose();
     }