Add Roadmap & Survey demo pages (#30951)

Author: dxvladislavvolkov

apps/demos/Demos/Chat/EmptyViewTemplate/[email protected]

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+With v25.2, you will be able to customize the Chat's empty view using our template engine. 
+
+<!--split-->
+Usage scenarios include: 
+- Onboarding & First-Time User Guidance. Display messages or tips to help new users start a conversation. You can also include UI elements that suggest prompts. 
+- Preliminary Information. Display important information before a conversation begins, such as usage instructions or data processing disclaimers. 
+- Context-Aware Messaging. Display dynamic content based on user context (for example, “Ask me anything about your current order”) for a more personalized experience. 
+- Branded Experience. Add brand visuals, mascots, or tone to engage users. 

apps/demos/Demos/Chat/EmptyViewTemplate/description.md

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+With v25.2, users will be able to attach files when sending messages through DevExtreme [Chat](https://js.devexpress.com/Documentation/Guide/UI_Components/Chat/Overview/).
+
+<!--split-->
+This feature will be of value for solutions that incorporate support conversations, team collaboration, and peer-to-peer communications.

apps/demos/Demos/Chat/FileAttachments/[email protected]

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+With v25.2, DevExtreme DataGrid will be able to display AI-generated columns. DataGrid will populate the AI column with auto-generated data based on component data and a custom prompt.
+<!--split-->
+Potential usage scenarios include: 
+- Data Enrichment. Add missing contextual information without modifying the underlying dataset. 
+- Categorization/Tagging. Assign categories or tags based on row information. 
+- Prediction & Estimation. Generate estimated delivery times, sale insights, or performance ratings (based on AI model).

apps/demos/Demos/Chat/FileAttachments/description.md

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+In v25.2, we will add a built-in [TagBox](https://js.devexpress.com/jQuery/Documentation/Guide/UI_Components/TagBox/Getting_Started_with_TagBox/) column to the DevExtreme DataGrid component. These columns allow users to select multiple values when editing cell content or specify multiple search criteria within the Filter Row.
+<!--split-->
+This feature enhances usability when working with multiple categories/related entities (such as tags, status info, or addresses). 

apps/demos/Demos/DataGrid/AIColumn/[email protected]

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+We will integrate AI-powered Smart Paste to DevExtreme [Form](https://js.devexpress.com/Documentation/Guide/UI_Components/Form/Overview/) and enhance traditional copy-paste workflows.
+
+<!--split-->
+When a user copies unstructured text (from spreadsheets, documents, emails, web pages, etc.) and activates Smart Paste, AI will analyze clipboard content and populate each form field with relevant data.