[FEATURE] expose GUI settings, not just color related, in templates

[rwx7]

Submission checklist

• I have searched existing issues and confirmed this has not been requested before.
• I have checked existing pull requests for similar changes.

Feature type

Configuration / customization

Feature summary

Expose useful noctalia variables in templates that change the look of noctalia bars.

corner_radius - match square or rounded borders
font_* - use same font and weight in title bars
alpha - match panel alpha. i have a minimap utility with transparent background and would like consistent look
margins
shadows - whether enabled and params
icon - icon set used

Motivation / use case

I want noctalia to drive all of the UX styling in my WM via a rendered user template file when wallpaper changes.

Proposed solution

I'm not C++ guy, but should be straightforward.

Alternatives considered

No response

References / related projects

No response

Additional context

No response