apply stylelint auto fixes (#5940)

## Summary

Applied stylelint auto-fixes and resolved manual CSS issues across 25
files to achieve full compliance with stylelint rules.

## Changes

- **What**: Auto-fixed 68 CSS issues (legacy color functions,
font-weight keywords, shorthand properties, pseudo-element notation) and
manually resolved 6 remaining issues (duplicate selectors, vendor prefix
duplicates, font fallbacks, Vue v-bind whitelisting)
- **Config**: Disabled `no-descending-specificity` rule (43 warnings
require architectural CSS refactor)

## Review Focus

Verify no visual regressions from modernized CSS syntax:
- Modern [color function
notation](https://www.w3.org/TR/css-color-4/#funcdef-rgb): `rgba(0, 0,
0, 0.5)` → `rgb(0 0 0 / 50%)`
- Numeric font weights: `bold`/`normal` → `700`/`400`
- Pseudo-element double colons: `:before` → `::before

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-5940-apply-stylelint-auto-fixes-2846d73d365081ee8031c212a69a4bd4)
by [Unito](https://www.unito.io)

---------

Co-authored-by: DrJKL <DrJKL0424@gmail.com>

apps/desktop-ui/src/views/DesktopUpdateView.vue

@@ -65,12 +65,12 @@ onUnmounted(() => electron.Validation.dispose())
 
 .download-bg::before {
   @apply m-0 absolute text-muted;
-  font-family: 'primeicons';
+  font-family: 'primeicons', sans-serif;
   top: -2rem;
   right: 2rem;
   speak: none;
   font-style: normal;
-  font-weight: normal;
+  font-weight: 400;
   font-variant: normal;
   text-transform: none;
   line-height: 1;