fix(frontend): align reward modal with shared runtime

assets/css/frontend/enhancements/components/custom-amount.css

@@ -1,54 +1,3 @@
-/* ---- custom amount ---- */
-.reward-custom {
-    display: flex;
-    align-items: center;
-    gap: 8px;
-    margin-bottom: 16px;
-}
-
-.reward-custom__input {
-    flex: 1;
-    height: 40px;
-    padding: 0 12px;
-    border: 1px solid var(--color-line, #e5e7eb);
-    border-radius: var(--radius, 10px);
-    background: var(--surface-2, #F4F5F7);
-    color: var(--color-ink);
-    font-size: 14px;
-    text-align: center;
-    outline: none;
-    transition: border-color 0.2s;
-    -moz-appearance: textfield;
-}
-
-.reward-custom__input::-webkit-inner-spin-button,
-.reward-custom__input::-webkit-outer-spin-button {
-    -webkit-appearance: none;
-    margin: 0;
-}
-
-.reward-custom__input:focus {
-    border-color: var(--color-primary, #f04494);
-}
-
-.reward-custom__confirm {
-    flex-shrink: 0;
-    height: 40px;
-    padding: 0 20px;
-    border: none;
-    border-radius: var(--radius, 10px);
-    background: var(--color-primary, #f04494);
-    color: #fff;
-    font-size: 14px;
-    font-weight: 500;
-    cursor: pointer;
-    transition: opacity 0.2s;
-}
-
-.reward-custom__confirm:hover {
-    opacity: 0.85;
-}
-
 /* ============================================================
  * 9. 公告跑马灯 Widget
  * ============================================================ */