Review and improve panel and panel-material-ui skills

[philippjfr]

Here I started reviewing the panel and panel-material-ui skills. For now these are fairly light edits:

• Decreasing the verbosity of the dependency section in panel
• Fixing a few typos
• Removing the incorrect "Linking Dashboard Theme with Page Theme" guidance (this is not necessary)
• Adding better guidance on the differences and uses of sx, theme_config, styles and stylesheets
• Adding information about the :material/icon: syntax

but I do have some questions and concerns that could lead to larger edits.

• Should the panel-material-ui skill really duplicate so much from the panel skill?
• Should we perhaps migrate out separate skills for things such as testing, optimizing, etc?
• Does the dependency section make sense at all?

@MarcSkovMadsen For you review.

[Copilot]

Pull request overview

This PR refines the documentation “skills” for panel and panel-material-ui, focusing on making the guidance clearer and less verbose while correcting small errors.

Changes:

• Simplified the dependency listings in skills/panel/SKILL.md.
• Updated/expanded guidance in skills/panel-material-ui/SKILL.md around theming/styling and icon usage, and removed incorrect theming synchronization guidance.
• Fixed minor typos and wording issues across both skill documents.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 5 comments.

File	Description
skills/panel/SKILL.md	Streamlines dependency descriptions and makes small guidance tweaks (reactivity, performance tip, typos).
skills/panel-material-ui/SKILL.md	Adds clearer theming/styling guidance, documents :material/...: usage, removes incorrect theming advice, and fixes small formatting/typo issues.