refactor(coordinator): sweep selectedTabIndex + bounds-check pattern across all extensions

[datlechin]

Summary

Completes the selectedTabAndIndex migration across 13 files / 30+ call sites. Closes the parking lot for this pattern. −104 / +81 LOC (net −23, but the more meaningful win is consistency: every active-tab lookup now uses one of two named helpers instead of the inline three-line pattern).

What was migrated

Every site that used guard let tabIndex = tabManager.selectedTabIndex, tabIndex < tabManager.tabs.count else { return } followed by let tab = tabManager.tabs[tabIndex]:

File	Methods
MainContentCoordinator.swift	runQuery, executeTableTabQueryDirectly, loadQueryIntoEditor, insertQueryFromAI, runExplainQuery, executeQueryInternal, handleSort, EXPLAIN error fallback
+ClickHouse.swift	runVariantExplain
+ColumnVisibility.swift	saveColumnVisibilityToTab
+Discard.swift	handleDiscard (two sites)
+ExecuteAll.swift	runAllStatements
+Favorites.swift	insertFavorite, runFavoriteInNewTab
+Filtering.swift	applyFilters, clearFiltersAndReload, restoreFiltersForTable
+FKNavigation.swift	navigateToFKReference (four sites)
+LoadMore.swift	loadMoreRows, fetchAllRows
+Navigation.swift	openTableTab (four sites), promotePreviewTab
+QueryParameters.swift	executeQueryWithParameters, executeQueryInternalParameterized, executeMultipleStatementsWithParameters
+Refresh.swift	handleRefresh (three sites)
MainContentCommandActions.swift	formatQuery, toggleResults, previousResultTab, nextResultTab

Pattern

• Write-back paths (need the index to mutate tabManager.tabs[i]): selectedTabAndIndex returning (tab, index).
• Read-only paths (only need the tab): selectedTab, plus an explicit (tab, _) from selectedTabAndIndex where strict bounds-check equivalence is preferred.
• Mixed paths (read tab properties, write back via index): (tab, tabIndex) destructured.

Behavior

Unchanged. Each migration preserves the original short-circuits (no tab selected, out-of-bounds, etc.) via selectedTabAndIndex's atomic bounds check. The minor exception was that read-only methods previously did tabs[index] after just an optional check — those now strictly bounds-check via selectedTabAndIndex, a tiny safety improvement.

The dispatchParameterizedStatements / dispatchStatements helpers (called via tabIndex parameter, not selectedTabIndex) were left alone — they take the index from the caller's already-validated lookup. ExecuteAll's tabIndex parameter pattern preserved.

Test plan

• Build clean
• Targeted tests pass (TableRowsMutationTests, SortCacheInvalidationTests, EvictionTests, QueryTabManagerSelectedTabAndIndexTests, RowOperationsDispatchTests)
• Manual: Cmd+Enter run query, Cmd+Shift+Enter run all, EXPLAIN
• Manual: open table from sidebar, FK navigation
• Manual: apply / clear filters, refresh (Cmd+R), discard dialog
• Manual: pagination Next/Prev
• Manual: format query (right-click), toggle results panel, insert favorite

What's next (parking lot, future PRs)

The selectedTabAndIndex pattern is now the canonical lookup. With it in place, the next coordinator dedup target would be:

• The confirmDiscardChangesIfNeeded callback pattern (used in Pagination, Filtering, Navigation — each captures its own copy of tabIndex/tabId via [weak self] then re-validates inside the callback). Could move to a per-action helper.
• The tabManager.tabs[tabIndex].execution.errorMessage = ... pattern for safe-mode error reporting (used 5+ times). Could become a setExecutionError(_:on:) helper on the coordinator.

Both warrant separate focused PRs.