feat: 设置页「添加插件」推荐目录 + 复制安装命令；移除内置 Office 预览

- 设置页侧边栏内容/文件预览两个网格末尾各增虚线卡片，弹出对应 kind 的插件弹窗
- 弹窗：GitHub topic 按钮（新标签页）+ 推荐插件目录（plugins-tabs.ts / plugins-viewers.ts）
- 每条目「跳转」（window.open 新标签页直达仓库）与「复制」（writeClipboard + 已复制反馈）
- 不做终端预填流：不关闭弹窗、不打开终端、无失败路径（install/installNotice/installError* 文案删除）
- 内置 Office 预览（docx/xlsx/pptx）整体移除，chunk 白名单 5→2（terminal/editor）
- 文案「内置插件」→「推荐插件」；AGENTS.md/README/设计文档同步

src/client/SideCardSection.module.css

@@ -198,6 +198,38 @@
   text-overflow: ellipsis;
 }
 
+/* The "add plugin" card: same grid cell / chrome as the inventory cards
+   (it shares .card), but a DASHED border — the repo's first dashed surface;
+   the hover accent follows the existing drag-drop dashed outlines
+   (sidebar.module.css .dropCenter / .tabBarDrop). */
+.addCard {
+  align-items: flex-start;
+  padding: 12px;
+  border-style: dashed;
+  border-color: var(--dsw-alias-border-l2);
+  text-align: left;
+}
+
+.addCard:hover {
+  background: var(--dsw-alias-interactive-bg-hover);
+  border-color: var(--dsw-alias-interactive-bg-hover-accent);
+  color: var(--dsw-alias-label-primary);
+}
+
+.addCard:hover .cardTitle {
+  color: var(--dsw-alias-label-primary);
+}
+
+.addCard:hover .cardIconChip {
+  border-color: color-mix(in srgb, var(--dsw-alias-button-primary-fill) 35%, transparent);
+  color: var(--dsw-alias-button-primary-fill);
+}
+
+.addCard:focus-visible {
+  outline: 2px solid var(--dsw-alias-border-l4);
+  outline-offset: 2px;
+}
+
 .cardOn .cardDesc {
   color: var(--dsw-alias-label-secondary);
 }
@@ -412,6 +444,179 @@
   color: var(--dsw-alias-state-error-primary);
 }
 
+/* ── "Add plugin" modal ──────────────────────────────────────────────── */
+
+/* A wide dialog like the settings popup (doubled class keeps the width
+   rule above the primitive's .dialog regardless of stylesheet order). */
+.pluginModal.pluginModal {
+  width: min(560px, 100%);
+}
+
+.pluginList {
+  display: flex;
+  flex-direction: column;
+  gap: 12px;
+  width: 100%;
+}
+
+/* The GitHub topic entry: a full-width secondary BUTTON (not a link — it
+   opens a real new browser tab via window.open, bypassing the sidebar
+   link takeover). */
+.pluginTopicBtn {
+  width: 100%;
+  appearance: none;
+  border: 1px solid var(--dsw-alias-border-l2);
+  border-radius: 8px;
+  padding: 6px 12px;
+  font: inherit;
+  font-size: 12px;
+  line-height: 18px;
+  color: var(--dsw-alias-label-secondary);
+  background: var(--dsw-alias-bg-layer-1);
+  cursor: pointer;
+}
+
+.pluginTopicBtn:hover {
+  background: var(--dsw-alias-interactive-bg-hover);
+  border-color: var(--dsw-alias-interactive-bg-hover-accent);
+  color: var(--dsw-alias-label-primary);
+}
+
+.pluginTopicBtn:focus-visible {
+  outline: 2px solid var(--dsw-alias-border-l4);
+  outline-offset: 1px;
+}
+
+.pluginEmpty {
+  padding: 20px 2px;
+  font-size: 12px;
+  line-height: 18px;
+  color: var(--dsw-alias-label-tertiary);
+}
+
+.pluginEntries {
+  display: flex;
+  flex-direction: column;
+  gap: 10px;
+}
+
+/* One catalog entry: name + install button on the head row, description,
+   then the install command in a mono block (the exact script that gets
+   pre-typed into the terminal — review it here before installing). */
+.pluginEntry {
+  display: flex;
+  flex-direction: column;
+  gap: 4px;
+  padding: 12px;
+  border: 1px solid var(--dsw-alias-border-l2);
+  border-radius: 12px;
+  background: var(--dsw-alias-bg-layer-1);
+}
+
+.pluginEntryHead {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  gap: 12px;
+}
+
+.pluginEntryActions {
+  display: inline-flex;
+  align-items: center;
+  gap: 6px;
+  flex: none;
+}
+
+/* The per-entry "jump" button: opens the plugin repo in a REAL new browser
+   tab (window.open — a button, so the sidebar link takeover cannot reroute
+   it). Secondary style, quieter than the Install button. */
+.pluginJumpBtn {
+  flex: none;
+  appearance: none;
+  border: 1px solid var(--dsw-alias-border-l2);
+  border-radius: 8px;
+  padding: 3px 12px;
+  font: inherit;
+  font-size: 12px;
+  line-height: 1.5;
+  cursor: pointer;
+  background: transparent;
+  color: var(--dsw-alias-label-secondary);
+}
+
+.pluginJumpBtn:hover {
+  background: var(--dsw-alias-interactive-bg-hover);
+  border-color: var(--dsw-alias-interactive-bg-hover-accent);
+  color: var(--dsw-alias-label-primary);
+}
+
+.pluginJumpBtn:focus-visible {
+  outline: 2px solid var(--dsw-alias-border-l4);
+  outline-offset: 1px;
+}
+
+.pluginName {
+  min-width: 0;
+  font-size: 13px;
+  line-height: 20px;
+  font-weight: 600;
+  color: var(--dsw-alias-label-primary);
+  text-decoration: none;
+  overflow: hidden;
+  text-overflow: ellipsis;
+  white-space: nowrap;
+}
+
+.pluginName:hover {
+  text-decoration: underline;
+  color: var(--dsw-alias-button-primary-fill);
+}
+
+.pluginDesc {
+  font-size: 12px;
+  line-height: 18px;
+  color: var(--dsw-alias-label-secondary);
+}
+
+.pluginInstall {
+  display: block;
+  padding: 6px 10px;
+  font-family: ui-monospace, SFMono-Regular, Menlo, monospace;
+  font-size: 11px;
+  line-height: 16px;
+  color: var(--dsw-alias-label-secondary);
+  background: var(--dsw-alias-bg-layer-2);
+  border: 1px solid var(--dsw-alias-border-l1);
+  border-radius: 8px;
+  overflow-x: auto;
+  white-space: nowrap;
+}
+
+/* The per-entry copy button: copies the install script to the
+   clipboard (the settings primary-button recipe, smaller than .done). */
+.pluginCopyBtn {
+  flex: none;
+  appearance: none;
+  border: 1px solid transparent;
+  border-radius: 8px;
+  padding: 3px 12px;
+  font: inherit;
+  font-size: 12px;
+  line-height: 1.5;
+  cursor: pointer;
+  background: var(--dsw-alias-label-primary);
+  color: var(--dsw-alias-bg-layer-3);
+}
+
+.pluginCopyBtn:hover {
+  background: var(--dsw-alias-button-primary-hover);
+}
+
+.pluginCopyBtn:focus-visible {
+  outline: 2px solid var(--dsw-alias-brand-primary);
+  outline-offset: 1px;
+}
+
 @media (prefers-reduced-motion: reduce) {
   .card,
   .switchTrack,