Convert the remaining dynamic and hardcoded inline styles to Tailwind utilities

Second styling pass over the components and pages: move conditional theme colors into className ternaries (bg-accent / bg-surface-hover etc.), turn reused CSSProperties constants into className constants, and express static hardcoded hex/rgba colors as Tailwind arbitrary values so the exact rendered colour is preserved. Truly dynamic styling (computed geometry, gradients, multi-part shadows, data-driven colours, the undefined --sidebar/--nav layout vars) stays inline as it cannot be expressed as a static class. Updated three component tests that asserted the old inline active-state styles to assert the equivalent utility class instead.

Verified: client typecheck 0, full client suite green, and a live light/dark render check in the dev server confirms the semantic theme tokens resolve correctly (the earlier 'transparent popups' were a stale dev server that pre-dated the tailwind.config token addition, not a code issue).

client/src/components/Settings/Section.tsx

@@ -9,10 +9,10 @@ interface SectionProps {
 
 export default function Section({ title, icon: Icon, children }: SectionProps): React.ReactElement {
   return (
-    <div className="rounded-xl border overflow-hidden" style={{ background: 'var(--bg-card)', borderColor: 'var(--border-primary)', marginBottom: 24 }}>
-      <div className="px-6 py-4 border-b flex items-center gap-2" style={{ borderColor: 'var(--border-secondary)' }}>
-        <Icon className="w-5 h-5" style={{ color: 'var(--text-secondary)' }} />
-        <h2 className="font-semibold" style={{ color: 'var(--text-primary)' }}>{title}</h2>
+    <div className="rounded-xl border overflow-hidden bg-surface-card border-edge" style={{ marginBottom: 24 }}>
+      <div className="px-6 py-4 border-b flex items-center gap-2 border-edge-secondary">
+        <Icon className="w-5 h-5 text-content-secondary" />
+        <h2 className="font-semibold text-content">{title}</h2>
       </div>
       <div className="p-6 space-y-4">
         {children}