style(ui): 操作按钮改幽灵样式——平时仅图标，悬停出底

- .act/.op 去底色边框，悬停浅灰底，危险按钮悬停淡红底+红字
- 用户/模型/兑换码/违禁词/并发分组/渠道六页统一

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Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

frontend/src/views/ConcurrencyView.vue

@@ -137,14 +137,13 @@ onMounted(load)
 <style scoped>
 .act {
   display: inline-flex; align-items: center; justify-content: center;
-  width: 1.9rem; height: 1.9rem; border-radius: 0.5rem;
-  color: var(--fg-2); background: var(--surface-2);
-  box-shadow: inset 0 0 0 1px var(--hairline);
+  width: 1.9rem; height: 1.9rem; border-radius: 0.6rem;
+  color: var(--fg-3); background: transparent;
   transition: background 0.15s, color 0.15s;
 }
 .act:hover { background: var(--hover); color: var(--fg); }
-.act.danger { color: rgb(253 164 175); background: rgb(244 63 94 / 0.12); box-shadow: inset 0 0 0 1px rgb(244 63 94 / 0.3); }
-.act.danger:hover { color: white; background: rgb(244 63 94 / 0.25); }
+.act.danger:hover { background: rgb(244 63 94 / 0.1); color: #dc2626; }
+
 .fade-enter-active, .fade-leave-active { transition: opacity 0.15s ease; }
 .fade-enter-from, .fade-leave-to { opacity: 0; }
 </style>