* feat(titlebar): selectable window button styles + minimize toggle
Custom title bar (Linux) gains a window-button style picker, mirroring
the seekbar style picker pattern. Six form-named styles: dots, dotsGlyph,
flat, pill, outline, glyph. All buttons now carry minimize/maximize/close
glyphs for clear, colour-blind-friendly iconography; dots reveal glyphs on
hover, dotsGlyph always shows them.
- New authStore state windowButtonStyle (default dots) + showMinimizeButton,
with rehydrate validation falling back to dots on unknown values.
- WindowButtonPreview reuses the real .titlebar-btn classes for WYSIWYG tiles.
- Picker + minimize toggle render under the Custom title bar setting, gated
on the toggle being on.
- Monochrome styles use --text-primary glyphs and stronger borders for
contrast on dark themes.
- Dev-build grey marker scoped to the real title bar so previews show true
colours.
- i18n keys in all 9 locales; setter and rehydrate tests.
* docs(changelog): window button styles (#1083)
Psychotoxical
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