fix: prevent sidebar clearing when opening new query tab (#576)

Two fixes:

1. EditorTabPayload.isConnectionOnly now excludes isNewTab payloads.
   The "+" button creates a payload with isNewTab:true which was
   incorrectly classified as connection-only, causing initializeAndRestoreTabs
   to skip the proper new-tab path and potentially fall into restoreFromDisk
   which clears session.tables.

2. Skip loadSchemaIfNeeded() when other windows already exist for the
   same connection. The schema is already loaded by the first window,
   and the concurrent driver use (schema load + health monitor ping)
   can crash single-connection drivers like MySQL on high-latency
   Cloud connections.

Author: datlechin

TablePro/Models/Query/EditorTabPayload.swift

@@ -93,8 +93,10 @@ internal struct EditorTabPayload: Codable, Hashable {
     /// Whether this payload is a "connection-only" payload — just a connectionId
     /// with no specific tab content. Used by MainContentView to decide whether
     /// to create a default tab or restore tabs from storage.
+    /// Note: isNewTab payloads (from the "+" button) are NOT connection-only —
+    /// they are explicit requests to open a new query tab.
     internal var isConnectionOnly: Bool {
-        tabType == .query && tableName == nil && initialQuery == nil
+        tabType == .query && tableName == nil && initialQuery == nil && !isNewTab
     }
 
     /// Create a payload from a persisted QueryTab for restoration

TablePro/Views/Main/MainContentView.swift

@@ -450,7 +450,13 @@ struct MainContentView: View {
     private func initializeAndRestoreTabs() async {
         guard !hasInitialized else { return }
         hasInitialized = true
-        Task { await coordinator.loadSchemaIfNeeded() }
+
+        // Only load schema if this is the first window for this connection.
+        // Additional windows share the same driver — concurrent schema load
+        // races with health monitor pings and can crash single-connection drivers.
+        if !WindowLifecycleMonitor.shared.hasOtherWindows(for: connection.id, excluding: windowId) {
+            Task { await coordinator.loadSchemaIfNeeded() }
+        }
 
         // If payload provided a specific tab (not connection-only), execute its query immediately
         if let payload, !payload.isConnectionOnly {