feat: 全站评论开关，并统一后台表单控件

关闭评论后前台隐藏评论能力；外观/设置/公告改用 AdminField 与 Stepper。

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/app/globals.css

@@ -1512,6 +1512,47 @@ h1, h2, h3, h4 {
 .j13-chat-composer-input.has-value::placeholder {
   color: transparent;
 }
+
+/* 后台输入：与聊天搜索同一套壳层聚焦（未分层，才能压过全局 :focus-visible 双线） */
+.admin-field-shell,
+.admin-stepper {
+  background: var(--bg);
+  border: 1px solid var(--line);
+  border-radius: 12px;
+  transition: border-color 0.15s ease, box-shadow 0.15s ease, background 0.15s ease;
+}
+.admin-field-shell:hover:not(:focus-within),
+.admin-stepper:hover:not(:focus-within) {
+  border-color: color-mix(in srgb, var(--line-2) 40%, var(--line));
+}
+.admin-field-shell:focus-within,
+.admin-stepper:focus-within {
+  border-color: var(--accent) !important;
+  box-shadow: 0 0 0 3px var(--accent-soft);
+  background: var(--panel);
+}
+.admin-field-input,
+.admin-field-input:focus,
+.admin-field-input:focus-visible,
+.admin-stepper-input,
+.admin-stepper-input:focus,
+.admin-stepper-input:focus-visible {
+  outline: none !important;
+  box-shadow: none !important;
+  border: 0 !important;
+  background: transparent !important;
+}
+.admin-stepper-btn:focus,
+.admin-stepper-btn:focus-visible {
+  outline: none !important;
+  box-shadow: none !important;
+}
+.admin-field-shell.is-invalid {
+  border-color: var(--danger) !important;
+}
+.admin-field-shell.is-invalid:focus-within {
+  box-shadow: 0 0 0 3px var(--danger-soft);
+}
 .j13-chat-composer-mirror {
   position: absolute;
   inset: 0;
@@ -1968,6 +2009,116 @@ a.j13-mention-token:hover {
     }
   }
 
+  .admin-field-head {
+    display: flex;
+    align-items: baseline;
+    justify-content: space-between;
+    gap: 0.75rem;
+    margin-bottom: 0.5rem;
+  }
+  .admin-field-head .field-label {
+    margin-bottom: 0;
+  }
+  .admin-field-count {
+    font-size: 12px;
+    font-variant-numeric: tabular-nums;
+    color: var(--ink-3);
+    flex-shrink: 0;
+  }
+  .admin-field-shell {
+    display: flex;
+    align-items: center;
+    width: 100%;
+  }
+  .admin-field-shell.is-area {
+    display: block;
+  }
+  .admin-field-input {
+    width: 100%;
+    min-width: 0;
+    padding: 10px 12px;
+    color: var(--ink);
+    font-size: 14px;
+    line-height: 1.5;
+    font-family: var(--font-sans);
+  }
+  .admin-field-input::placeholder {
+    color: var(--ink-3);
+  }
+  .admin-field-input:disabled {
+    opacity: 0.6;
+    cursor: not-allowed;
+  }
+  textarea.admin-field-input {
+    display: block;
+    font-family: var(--font-sans);
+    font-size: 14px;
+    line-height: 1.7;
+    resize: vertical;
+  }
+  .admin-search-shell {
+    display: flex;
+    align-items: center;
+    gap: 0.5rem;
+    height: 2.5rem;
+    padding: 0 0.75rem;
+  }
+  .admin-search-shell .admin-field-input {
+    padding: 0;
+    height: 100%;
+    font-size: 13px;
+  }
+
+  .admin-stepper {
+    display: inline-flex;
+    align-items: stretch;
+    flex-shrink: 0;
+    height: 2.5rem;
+    overflow: hidden;
+  }
+  .admin-stepper.is-disabled {
+    opacity: 0.6;
+  }
+  .admin-stepper-btn {
+    display: inline-flex;
+    align-items: center;
+    justify-content: center;
+    width: 2.25rem;
+    border: none;
+    padding: 0;
+    background: transparent;
+    color: var(--ink-2);
+    cursor: pointer;
+  }
+  .admin-stepper-btn:hover:not(:disabled) {
+    background: var(--tint);
+    color: var(--ink);
+  }
+  .admin-stepper-btn:disabled {
+    opacity: 0.35;
+    cursor: not-allowed;
+  }
+  .admin-stepper-input {
+    width: 3.25rem;
+    min-width: 0;
+    padding: 0;
+    margin: 0;
+    text-align: center;
+    color: var(--ink);
+    font-size: 14px;
+    font-weight: 600;
+    font-variant-numeric: tabular-nums;
+    font-family: var(--font-sans);
+  }
+  .admin-stepper-unit {
+    display: inline-flex;
+    align-items: center;
+    padding-right: 0.25rem;
+    font-size: 12.5px;
+    color: var(--ink-3);
+    user-select: none;
+  }
+
   /* ----- 点赞按钮：未赞描边态，hover 同色系填充；已赞为浅底实心态 ----- */
   .j13-like {
     border-color: var(--line-2);
@@ -2593,7 +2744,7 @@ a.j13-mention-token:hover {
   .j13-pulse-cell:nth-child(odd) {
     border-right: 1px solid var(--line);
   }
-  .j13-pulse-cell:nth-child(-n + 2) {
+  .j13-pulse-cell:nth-child(-n + 2):nth-last-child(n + 3) {
     border-bottom: 1px solid var(--line);
   }
   .j13-pulse-lab {