refactor: add hasStructureChanges/isHistoryPanelVisible to ConnectionToolbarState

Migrated sidebar reads from AppState.shared to per-window coordinator.
Added two properties to ConnectionToolbarState for future write migration.
AppState.shared writes remain temporarily — removing them requires careful
per-file editing to avoid breaking multi-line expressions.

Author: datlechin

TablePro/Models/Connection/ConnectionToolbarState.swift

@@ -183,6 +183,12 @@ final class ConnectionToolbarState {
     /// Whether there are pending data grid changes (for SQL preview button)
     var hasDataPendingChanges: Bool = false
 
+    /// Whether the structure view has pending schema changes
+    var hasStructureChanges: Bool = false
+
+    /// Whether the history panel is visible
+    var isHistoryPanelVisible: Bool = false
+
     /// Whether the SQL review popover is showing
     var showSQLReviewPopover: Bool = false