docs: deprecate in favor of jbrowse-anywidget

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01GQgtH3gv6ccbLtoGT9FEPo

Author: cmdcolin

README.md

@@ -1,3 +1,16 @@
+> [!IMPORTANT]
+> **This project is deprecated and no longer maintained. Use
+> [jbrowse-anywidget](https://github.com/GMOD/jbrowse-anywidget) instead.**
+>
+> `jbrowse-anywidget` replaces the Dash-based stack here (and
+> [dash_jbrowse](https://github.com/GMOD/dash_jbrowse)) with an
+> [anywidget](https://anywidget.dev): no Dash server to run, one bundle that
+> renders in Jupyter, JupyterLab, VS Code, Colab, and marimo, and two-way sync
+> of the visible region between Python and the view.
+>
+> This repo stays online read-only so the links in
+> [the paper](https://doi.org/10.1093/bioinformatics/btad032) keep resolving.
+
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