Grids AI Assistant: Add Final Updates

[arman-boyakhchyan]

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[Copilot]

Pull request overview

This PR finalizes documentation updates for the Grids AI Assistant feature in the DevExtreme documentation set, aligning release notes and API reference pages with the latest state of the feature.

Changes:

• Updated v26.1 release notes to remove the “(CTP)” label from the “DataGrid and TreeList — AI Assistant” entry across jQuery/Angular/Vue/React sections.
• Extended predefined command documentation to include a mode: 'select' | 'deselect' argument for selectByIndexes.
• Added a named demo button include for the DataGrid AI Assistant demo to the shared AIAssistant type page and the DataGrid aiAssistant configuration page.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
concepts/Common/Whats New/00 v26.1 Release Notes.md	Removes “(CTP)” from AI Assistant release note entries across frameworks.
api-reference/40 Common Types/15 grids/PredefinedCommands/PredefinedCommands.md	Documents mode for selectByIndexes command arguments (common grids type).
api-reference/40 Common Types/15 grids/AIAssistant/AIAssistant.md	Adds a demo button link for the DataGrid AI Assistant demo to the shared AI Assistant type.
api-reference/10 UI Components/dxDataGrid/9 Types/DataGridPredefinedCommands/DataGridPredefinedCommands.md	Documents mode for selectByIndexes command arguments (DataGrid-specific type).
api-reference/10 UI Components/dxDataGrid/1 Configuration/aiAssistant/aiAssistant.md	Adds a demo button link for the DataGrid AI Assistant demo to the DataGrid option page.