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.h

@@ -34,6 +34,7 @@ public:
     int currentNodeIndex() const;
     void scrollToNodeId(uint64_t nodeId);
     void showFindBar();
+    void dismissHistoryPopup();
 
     // ── Column span computation ──
     static ColumnSpan typeSpan(const LineMeta& lm, int typeW = kColType);