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>

src/platform/updates/components/ReleaseNotificationToast.vue

@@ -172,7 +172,7 @@ onMounted(async () => {
   width: 448px;
   padding: 16px 16px 8px;
   background: #353535;
-  box-shadow: 0px 4px 4px rgba(0, 0, 0, 0.25);
+  box-shadow: 0 4px 4px rgb(0 0 0 / 0.25);
   border-radius: 12px;
   outline: 1px solid #4e4e4e;
   outline-offset: -1px;
@@ -193,7 +193,7 @@ onMounted(async () => {
   width: 42px;
   height: 42px;
   padding: 10px;
-  background: rgba(0, 122, 255, 0.2);
+  background: rgb(0 122 255 / 0.2);
   border-radius: 8px;
   display: flex;
   justify-content: center;

src/platform/updates/components/WhatsNewPopup.vue

@@ -218,7 +218,7 @@ defineExpose({
   width: 400px;
   outline: 1px solid #4e4e4e;
   outline-offset: -1px;
-  box-shadow: 0px 8px 32px rgba(0, 0, 0, 0.3);
+  box-shadow: 0 8px 32px rgb(0 0 0 / 0.3);
   position: relative;
 }
 
@@ -293,12 +293,6 @@ defineExpose({
   transform: translate(-50%, -50%) rotate(-45deg);
 }
 
-/* Content Section */
-.popup-content {
-  display: flex;
-  flex-direction: column;
-}
-
 .content-text {
   color: white;
   font-size: 14px;