refactor: convert color system to RGB channels for native Tailwind opacity

Root cause fix for all broken CSS variable opacity modifiers. Converted
every hex CSS variable to space-separated RGB channels (e.g. #fda4af →
253 164 175) and updated Tailwind config to use rgb(var(...) / <alpha-value>).
This makes bg-accent-rose/10, border-border-hard/50, etc. work natively
everywhere — no more currentColor fallback. Reverted all previous explicit
rgba() workarounds back to clean Tailwind syntax. Also fixed the voice
connection wifi icon SVG (was bottom-left aligned, now centered).

packages/web/src/components/modals/UserSettings.tsx

@@ -76,7 +76,7 @@ export function UserSettingsModal() {
         </div>
 
         {error && (
-          <div className="p-2 bg-[rgba(253,164,175,0.10)] border border-[rgba(253,164,175,0.30)] rounded text-txt-danger text-sm">{error}</div>
+          <div className="p-2 bg-accent-rose/10 border border-accent-rose/30 rounded text-txt-danger text-sm">{error}</div>
         )}
         {success && (
           <div className="p-2 bg-status-online/10 border border-status-online/30 rounded text-status-online text-sm">{success}</div>