fix: clear stale column focus memory on expel and absorb

When a tab moved between columns (expel/absorb), columnFocusedTab
still pointed to the moved tab's ID. focusLeft/focusRight would then
resolve to the wrong column, making Cmd+H appear stuck after expelling
a pane from the bottom of a column.

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

Author: bradjenn

Blink/Store/AppStore.swift

@@ -556,6 +556,11 @@ final class AppStore {
         cols[sourceIdx].tabIds.removeLast()
         cols[colIdx].tabIds.append(absorbedTabId)
 
+        // Clear stale focus memory if it pointed to the moved tab
+        if columnFocusedTab[cols[sourceIdx].id] == absorbedTabId {
+            columnFocusedTab.removeValue(forKey: cols[sourceIdx].id)
+        }
+
         // Remove source column if empty
         if cols[sourceIdx].tabIds.isEmpty {
             columnFocusedTab[cols[sourceIdx].id] = nil
@@ -579,6 +584,11 @@ final class AppStore {
         cols[sourceIdx].tabIds.removeLast()
         cols[colIdx].tabIds.append(absorbedTabId)
 
+        // Clear stale focus memory if it pointed to the moved tab
+        if columnFocusedTab[cols[sourceIdx].id] == absorbedTabId {
+            columnFocusedTab.removeValue(forKey: cols[sourceIdx].id)
+        }
+
         // Remove source column if empty
         if cols[sourceIdx].tabIds.isEmpty {
             columnFocusedTab[cols[sourceIdx].id] = nil
@@ -600,6 +610,9 @@ final class AppStore {
         // Remove tab from current column
         cols[colIdx].tabIds.removeAll { $0 == activeTabId }
 
+        // Clear stale focus memory — the expelled tab no longer lives in this column
+        columnFocusedTab.removeValue(forKey: currentCol.id)
+
         // Create new column to the right
         let newCol = Column(id: UUID().uuidString, tabIds: [activeTabId])
         cols.insert(newCol, at: cols.index(after: colIdx))