feat: 位置兼容模式支持自定义下移距离（齿轮弹窗数字输入）

titleBarStripPx 新偏好（0–120px，默认 40）：侧边栏按钮与内容的下移量改为
CSS 变量 --dsh-title-bar-strip 驱动，Sidebar shell 随 prefs 写入。设置页
「常规」的位置兼容模式行在开启时显示齿轮小图标，弹窗内用数字行设置下移
距离（复用 FeatureSettingsRows 行控件与提交钳制）。

src/client/SideCardSection.tsx

@@ -52,6 +52,8 @@ import type {} from '@deepseek-ai/dsh-client-ui-settings/client'
 import type { PropsRuntime } from '@deepseek-ai/dsh-client-ui-slots'
 import {
   clampWidthPercent,
+  TITLE_BAR_STRIP_MAX,
+  TITLE_BAR_STRIP_MIN,
   WIDTH_PERCENT_MAX,
   WIDTH_PERCENT_MIN,
   type SidebarPrefs,
@@ -380,6 +382,8 @@ export function SideCardSection({ store, service }: SideCardSectionProps) {
   const [error, setError] = useState<string | null>(null)
   // Which feature's secondary settings popup is open (null = closed).
   const [settingsFor, setSettingsFor] = useState<TabDescriptor | FileViewerDescriptor | null>(null)
+  // Whether the position-compat strip popup (the gear on the 常规 row) is open.
+  const [stripSettingsOpen, setStripSettingsOpen] = useState(false)
   // Whether the "add plugin" modal (a dashed card at the end of the
   // 侧边栏内容 / 文件预览 grids) is open, and for which extension point
   // (null = closed).
@@ -665,11 +669,30 @@ export function SideCardSection({ store, service }: SideCardSectionProps) {
             <span className={css.title}>{t('settingsTitleBarTitle')}</span>
             <span className={css.desc}>{t('settingsTitleBarDesc')}</span>
           </span>
-          <Switch
-            label={t('settingsTitleBarTitle')}
-            checked={prefs.titleBarCompat}
-            onChange={(next) => { applyPref({ titleBarCompat: next }) }}
-          />
+          <span className={css.control}>
+            {/*
+              The position-compat row's gear (same popup pattern as the
+              feature cards): opens a Modal with the strip-height number row.
+              Hidden while the mode is off — its related setting is dormant
+              then (the feature-card convention).
+            */}
+            {prefs.titleBarCompat && (
+              <button
+                type="button"
+                className={css.rowGear}
+                aria-label={`${t('settingsTitleBarTitle')} ${t('settingsPopup')}`}
+                title={t('settingsPopup')}
+                onClick={() => { setStripSettingsOpen(true) }}
+              >
+                <IconSettingsOutline16 size={14} />
+              </button>
+            )}
+            <Switch
+              label={t('settingsTitleBarTitle')}
+              checked={prefs.titleBarCompat}
+              onChange={(next) => { applyPref({ titleBarCompat: next }) }}
+            />
+          </span>
         </div>
       </div>
 
@@ -794,6 +817,41 @@ export function SideCardSection({ store, service }: SideCardSectionProps) {
         </Modal>
       )}
 
+      {/* The position-compat strip popup (opened by the gear on the 常规
+          row): one number row for the reserved strip height in px. Same
+          Modal chrome and row machinery as the feature popups — mounted
+          only while open (the Modal SSR rule above). */}
+      {stripSettingsOpen && (
+        <Modal
+          open
+          onClose={() => { setStripSettingsOpen(false) }}
+          title={t('settingsTitleBarTitle')}
+          description={t('settingsPopupDesc', { feature: t('settingsTitleBarTitle') })}
+          closeLabel={t('close')}
+          className={css.popupDialog}
+          footer={(
+            <button type="button" className={css.done} onClick={() => { setStripSettingsOpen(false) }}>
+              {t('settingsDone')}
+            </button>
+          )}
+        >
+          <FeatureSettingsRows
+            toggles={[{
+              key: 'titleBarStripPx',
+              type: 'number',
+              title: () => t('settingsTitleBarStripTitle'),
+              desc: () => t('settingsTitleBarStripDesc'),
+              min: TITLE_BAR_STRIP_MIN,
+              max: TITLE_BAR_STRIP_MAX,
+              unit: 'px',
+            }]}
+            prefs={prefs}
+            onToggle={onToggleSetting}
+            onCommit={onCommitSetting}
+          />
+        </Modal>
+      )}
+
       {/* The "add plugin" modal (opened by the dashed cards above): declares
           the extension point of the clicked kind, opens the GitHub topic,
           and lists the matching recommended plugin catalog with per-entry