chore(comments): tighten v1.4.10 inline commentary after self-review

Five trim spots from the cycle's earlier commits — none change behaviour,
just drop redundant phrasing and stale references per the HellionChat
comment-style convention (1-3 lines default, link "same as X" instead of
repeating, file:line refs only where they aid navigation).

SymbolPicker:
- BmpWhitelist header consolidated to source + filter ranges
- ImRaii.Popup pattern links the established ChatLogWindow popup idiom
  instead of citing three call-sites
- ToIconString comment drops the "discoverability" footnote that the
  code already telegraphs
- Manually-wrapping comment drops the "same modern idiom" tail that
  duplicated the preceding sentence

MessageStore:
- Merge the stale pre-v1.4.10 sqlScanLimit comment with the new
  v1.4.10 commentary; the cap mention now describes the historical
  reason rather than a parameter that no longer exists

HellionChat/MessageStore.cs

@@ -997,17 +997,12 @@ internal class MessageStore : IDisposable
         }
     }
 
-    // Returns up to limit tells exchanged with the named player, oldest-first.
-    // SQL narrows by Receiver + ChatType (indexed); client does the final
-    // PlayerPayload comparison. sqlScanLimit caps the scan to stay within
-    // the message-processing worker thread budget.
-    // Walks the full receiver-filtered tell history newest-first and stops
-    // as soon as the per-partner match count reaches `limit`. The previous
-    // hardcoded 500-row scan window cut active users' less-frequent pinned
-    // partners out of the result whenever other partners' chatter pushed
-    // them off the back of the window. Index on (Receiver, Date) keeps the
-    // SQL side cheap; the client-side break bounds the actual decode cost
-    // to roughly the depth at which `limit` partner matches accumulate.
+    // Returns up to `limit` tells exchanged with the named player, oldest-first.
+    // SQL narrows by Receiver + ChatType via the (Receiver, Date) index, then
+    // the client-side loop runs PlayerPayload comparison and breaks once
+    // `limit` partner matches accumulate. Earlier versions had a hardcoded
+    // 500-row scan cap that cut less-frequent pinned partners off the back of
+    // the window in chatty sessions; removed in v1.4.10.
     internal IReadOnlyList<Message> GetTellHistoryWithSender(
         ulong receiver,
         string senderName,