fix(deps): unpin param and panel

Koushik Kumaranrequested to merge
357-unpin-param into main

panel 1.9.0 changed Layoutable.stylesheets to param.List(item_type=str), rejectin bokeh.models.css.ImportedStyleSheet objects. Update get_stylesheet() to return the URL string directly; panel wraps it internally.

Closes #357 (closed)

Co-Authored-By: Claude Sonnet 4.6 noreply@anthropic.com

Edited by Koushik Kumaran

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