feat(frontend): regroup settings dialog, icon renderer tiles

Settings splits into labelled sections — renderer, appearance, wallpaper
and CSS, notifications, auth, backup — each with an icon header. Renderer
options gain a per-style glyph and accent-highlighted selection; theme
becomes a segmented Dark/Light control; the dialog widens to max-w-xl.

Renderer switching itself verified working end-to-end (live switch +
persistence across reload); unchanged code path since v2.0.0.

Authored By: TDvorak <[email protected]>

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

CHANGELOG.md

@@ -8,6 +8,10 @@ All notable changes to Dash. Format follows
 
 ### Changed
 
+- Settings dialog regrouped into icon-labelled sections (renderer, appearance,
+  wallpaper/CSS, notifications, auth, backup); renderer tiles now show a
+  per-style glyph and the theme picker is a segmented control
+
 - Monitoring charts restyled to the Beszel school: titled chart cards with
   subtitles, soft area fills on a true time-scaled axis, unit-aware Y ticks,
   sorted dotted tooltips, and legend chips on multi-series charts