refactor: replace hardcoded rgba/hex colors with Tailwind tokens

- rgba(255,255,255,0.xx) → bg-white/[0.xx], border-white/[0.xx]
- rgba(6,182,212,0.3) → border-primary/30 (focus states)
- #0a0a0a → bg-background
- Inline style hex colors → var(--color-primary), var(--color-brand-gradient-to)
- 28 files updated, zero hardcoded rgba() patterns remaining

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/pages/AssistantChatPage.tsx

@@ -223,7 +223,7 @@ export default function AssistantChatPage() {
                   <div className="w-8 h-8 rounded-full bg-primary/15 flex items-center justify-center">
                     <Sparkles size={14} className="text-primary" />
                   </div>
-                  <div className="bg-[rgba(255,255,255,0.04)] border border-brand-border rounded-2xl px-4 py-3">
+                  <div className="bg-white/[0.04] border border-brand-border rounded-2xl px-4 py-3">
                     <Loader2 size={16} className="animate-spin text-primary" />
                   </div>
                 </div>
@@ -242,7 +242,7 @@ export default function AssistantChatPage() {
                     onKeyDown={handleKeyDown}
                     placeholder="Ask about IT, networking, troubleshooting..."
                     rows={3}
-                    className="flex-1 resize-none rounded-xl border bg-card text-foreground text-sm placeholder:text-muted-foreground px-4 py-3 focus:outline-hidden focus:border-[rgba(6,182,212,0.3)]"
+                    className="flex-1 resize-none rounded-xl border bg-card text-foreground text-sm placeholder:text-muted-foreground px-4 py-3 focus:outline-hidden focus:border-primary/30"
                     style={{ borderColor: 'var(--glass-border)' }}
                     disabled={loading}
                   />