Add quality gates: Prettier for Astro, astro check for shared, unused SCSS variable lint (#2749)

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>

shared/ui/AvatarUpload.astro

@@ -1,22 +1,17 @@
 ---
 // Equivalent of ui/avatar-upload.html
-import Icon from './Icon.astro';
+import Icon from './Icon.astro'
 
 interface Props {
-	class?: string;
-	size?: string;
+  class?: string
+  size?: string
 }
 
-const { class: className, size } = Astro.props;
+const { class: className, size } = Astro.props
 
-const classes = [
-	'avatar',
-	'avatar-upload',
-	className,
-	size && `avatar-${size}`,
-]
+const classes = ['avatar', 'avatar-upload', className, size && `avatar-${size}`]
 ---
 
 <a href="#" class:list={classes}>
-	<Icon name="plus" />
+  <Icon name="plus" />
 </a>