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/voice/VoiceControls.tsx

@@ -115,7 +115,7 @@ export function VoiceControls() {
           title="Connection Info"
         >
           <svg width="20" height="20" viewBox="0 0 24 24" fill="currentColor" className={qualityColor}>
-            <path d="M1.5 21.5a1.5 1.5 0 100-3 1.5 1.5 0 000 3zM3.14 15.75a.75.75 0 01-.09-1.06A8.46 8.46 0 0112 11a8.46 8.46 0 018.95 3.69.75.75 0 01-1.15.97A6.96 6.96 0 0012 12.5a6.96 6.96 0 00-7.8 3.16.75.75 0 01-1.06.09zM6.37 18.3a.75.75 0 01-.08-1.06A5.46 5.46 0 0112 15a5.46 5.46 0 015.71 2.24.75.75 0 01-1.14.97A3.96 3.96 0 0012 16.5a3.96 3.96 0 00-4.57 1.71.75.75 0 01-1.06.09z" />
+            <path d="M1 9l2 2c4.97-4.97 13.03-4.97 18 0l2-2C16.93 2.93 7.08 2.93 1 9zm8 8l3 3 3-3c-1.65-1.66-4.34-1.66-6 0zm-4-4l2 2c2.76-2.76 7.24-2.76 10 0l2-2C15.14 9.14 8.87 9.14 5 13z" />
           </svg>
         </button>
 

packages/web/src/components/voice/VoiceGrid.tsx

@@ -134,7 +134,7 @@ export function VoiceGrid({ participants }: VoiceGridProps) {
 
         {/* Bottom strip of other tiles */}
         {!stripHidden && otherTiles.length > 0 && (
-          <div className="h-[120px] flex-shrink-0 flex items-center justify-center gap-2 p-2 bg-[rgba(11,11,16,0.50)] overflow-x-auto no-scrollbar">
+          <div className="h-[120px] flex-shrink-0 flex items-center justify-center gap-2 p-2 bg-surface-base/50 overflow-x-auto no-scrollbar">
             {otherTiles.map((t) => (
               <div
                 key={t.key}