fix: redesign buttons — depth, outline contrast, press effect

- button.tsx: primary gets gradient + shadow + hover glow + -translate-y-px
  lift; outline gets border-2 for visibility on dark bg; all variants
  get active:scale-[0.96] press feel; lg size h-12 for auth forms
- Remove hardcoded bg-[var(--accent)] overrides from Login, Register,
  Feed, Profile, Upload — variants now handle all coloring

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

client/src/pages/ProfilePage.tsx

@@ -167,7 +167,7 @@ export default function ProfilePage() {
               <Link to="/upload">
                 <Button
                   size="sm"
-                  className="rounded-xl text-xs h-8 gap-1.5 bg-[var(--accent)] hover:bg-[var(--accent-hover)] text-white px-4 shadow-sm"
+                  size="sm" className="gap-1.5"
                 >
                   <Plus className="h-3.5 w-3.5" strokeWidth={2.5} />
                   Новая публикация
@@ -198,7 +198,7 @@ export default function ProfilePage() {
           </p>
           {isMe && (
             <Link to="/upload">
-              <Button size="sm" className="rounded-xl text-xs bg-[var(--accent)] hover:bg-[var(--accent-hover)] text-white">
+              <Button size="sm">
                 Загрузить кота
               </Button>
             </Link>