fix: remove value history cooldown hack, dismiss popup on clear

The cooldown suppressed tracking for ~1s but the popup persisted showing
stale "1h ago" values because applyDocument skips popup dismissal.
Replaced with explicit dismissHistoryPopup() after clear+refresh so the
popup is gone immediately. Value tracking resumes on the next async cycle
with a clean baseline (m_refreshGen++ discards in-flight reads,
m_prevPages.clear() prevents phantom diffs).

src/editor.cpp

@@ -1387,6 +1387,11 @@ void RcxEditor::showFindBar() {
     m_findPos = 0;
 }
 
+void RcxEditor::dismissHistoryPopup() {
+    if (m_historyPopup)
+        static_cast<ValueHistoryPopup*>(m_historyPopup)->dismiss();
+}
+
 void RcxEditor::hideFindBar() {
     m_findBarContainer->setVisible(false);
     long docLen = m_sci->SendScintilla(QsciScintillaBase::SCI_GETLENGTH);