Give readable content its own text size (#3637)

* feat(app): separate content typography from interface size

Readable prose benefits from its own scale without inflating navigation and controls. Preserve existing users’ rendered size during migration while giving fresh desktop installs a 15px content default.

* test(app): cover independent content typography

The appearance journey now verifies that changing interface size leaves content size intact. Timeline traversal yields when a test deliberately holds the requested page, so the helper no longer waits on its own gate.

* test(desktop): cover independent content typography

The desktop appearance regression follows the renamed Interface control and verifies it does not alter Content size.

packages/app/src/i18n/resources/zh-CN.ts

@@ -2023,12 +2023,17 @@ export const zhCN: TranslationResources = {
         interfaceFont: "界面字体",
         interfaceFontHint: "用于整个应用。留空则使用系统默认",
         interfaceFontAccessibility: "界面字体族",
-        baseSize: "基础字号",
-        baseSizeAccessibility: "基础字号",
+        interfaceSize: "界面字号",
+        interfaceSizeHint: "用于导航、控件和标签",
+        interfaceSizeAccessibility: "界面字体大小",
+        contentSize: "内容字号",
+        contentSizeHint: "用于聊天文本和渲染后的 Markdown",
+        contentSizeAccessibility: "内容字体大小",
         codeFont: "代码字体",
         codeFontHint: "用于代码、diff 和终端输出。留空则使用系统默认",
         codeFontAccessibility: "代码字体族",
         codeSize: "代码字号",
+        codeSizeHint: "用于代码、差异和终端输出",
         codeSizeAccessibility: "代码字号",
       },
       syntax: {
@@ -2036,7 +2041,8 @@ export const zhCN: TranslationResources = {
         highlightTheme: "高亮主题",
         highlightThemeHint: "代码配色，独立于应用主题",
         highlightThemeAccessibility: "高亮主题：{{value}}",
-        previewAccessibility: "语法主题和代码字体的实时预览",
+        previewAccessibility: "内容排版、语法主题和代码字体的实时预览",
+        previewContent: "内容和代码预览",
       },
     },
     shortcuts: {