Add deprecation notice to README

[gnandretta]

Add deprecation notice to README

Summary

Added a deprecation notice to the README.md file to inform users that the atom-js project is no longer maintained. The notice was placed immediately after the title and before the existing description, as requested for ticket COG-19.

Changes:

• Added > **DEPRECATED**: This project is no longer maintained. as a blockquote after the main title
• Preserved all existing documentation content below the notice

Review & Testing Checklist for Human

• Verify the deprecation notice renders correctly as a blockquote on GitHub
• Confirm the notice is positioned appropriately (after title, before description)
• Check that the deprecation message tone is professional and appropriate

Recommended test plan:

1. View the README.md file on GitHub to ensure proper markdown rendering
2. Verify all existing documentation content remains intact and readable

---

Diagram

%%{ init : { "theme" : "default" }}%%
graph TD
    README["README.md<br/>Main documentation file"]:::major-edit
    
    subgraph Legend
        L1[Major Edit]:::major-edit
        L2[Minor Edit]:::minor-edit
        L3[Context/No Edit]:::context
    end
    
    classDef major-edit fill:#90EE90
    classDef minor-edit fill:#87CEEB
    classDef context fill:#FFFFFF

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Notes

• This is a documentation-only change with minimal risk
• The deprecation notice follows standard markdown blockquote formatting
• All existing documentation content has been preserved
• Part of COG-19 ticket requirements
• Session requested by Gabriel Andretta (@gnandretta)
• Link to Devin run: https://staging.itsdev.in/sessions/d504985406a74bb1a1f8cc5ecf07e7bb

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