fix(datagrid): Delete multi-select, filter panel redesign, Cmd+R refresh

[J2TeamNNL]

Summary

• D12A — Delete key now reads gridSelection.affectedRows first before falling back to selectedRowIndexes, matching the existing copy() pattern. validateUserInterfaceItem and deleteSelectedRowsIfPossible updated accordingly.
• D12B — rightMouseDown override in KeyHandlingTableView: when the clicked row is already inside the selection, the override skips super (which would collapse the selection) and calls NSMenu.popUpContextMenu directly.
• D13 — Filter panel redesign per owner spec: "Unset" renamed to "Clear" (calls clearAppliedFilters() — keeps filter rows, returns table to unfiltered); per-row Apply/Applied buttons removed; "Apply Only This Filter" moved to each row's context menu; tri-state checkbox added to panel header to toggle all rows enabled/disabled; "Remove All Filters" added to the ... options menu (calls clearFilterState()).
• D14 — After currentQueryTask?.cancel(), immediately set currentQueryTask = nil and reset tab.execution.isExecuting = false so runQuery() is not blocked by the guard check.

Test plan

• Select multiple rows with Shift/Cmd click, press Delete — all selected rows should be marked for deletion
• Select cells across rows via drag (grid selection), press Delete — affected rows should be marked for deletion
• Select multiple rows, right-click a row inside the selection — context menu appears without collapsing the selection
• Filter panel: click "Clear" — filter rows remain, table reloads without filters applied
• Filter panel ... menu: click "Remove All Filters" — all filter rows removed, table reloads without filters
• Filter panel: right-click a row, choose "Apply Only This Filter" — only that row's filter is applied
• Filter panel header checkbox: with mixed enabled state shows dash icon; clicking enables all; clicking again disables all
• While a query is executing, press Cmd+R — query cancels and a fresh query starts immediately

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Avoid clearing the running task before restarting

When Cmd+R is pressed while a table query is still running, these lines discard the only currentQueryTask reference and mark the tab idle before runQuery() starts the replacement. The canceled task can still be inside queryExecutor.executeQuery; when it later observes cancellation, executeQueryInternal calls resetExecutionState(...), which unconditionally sets isExecuting = false and currentQueryTask = nil for the tab, thereby clearing the newly-started refresh task's UI/task state. Because the task reference is nil before executeQueryInternal runs, its existing cancelQuery() path is also skipped for this refresh case.

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[J2TeamNNL]

Splitting into separate PRs per fix (D12, D13, D14).