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/chat/MarkdownRenderer.tsx

@@ -67,8 +67,8 @@ const aetherTheme = {
   ...themes.oneDark,
   plain: {
     ...themes.oneDark.plain,
-    backgroundColor: 'var(--bg-elevated)',
-    color: 'var(--text-message)',
+    backgroundColor: 'rgb(var(--bg-elevated))',
+    color: 'rgb(var(--text-message))',
   },
 };