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/hooks/use-settings/index.ts

@@ -16,13 +16,16 @@ import {
   DEFAULT_APP_SETTINGS,
   DEFAULT_CLIENT_SETTINGS,
   DEFAULT_CODE_FONT_SIZE,
+  DEFAULT_CONTENT_FONT_SIZE,
   DEFAULT_TERMINAL_SCROLLBACK_LINES,
   DEFAULT_THEME_PREFERENCE,
   DEFAULT_UI_BASE_FONT_SIZE,
   MAX_CODE_FONT_SIZE,
+  MAX_CONTENT_FONT_SIZE,
   MAX_TERMINAL_SCROLLBACK_LINES,
   MAX_UI_BASE_FONT_SIZE,
   MIN_CODE_FONT_SIZE,
+  MIN_CONTENT_FONT_SIZE,
   MIN_TERMINAL_SCROLLBACK_LINES,
   MIN_UI_BASE_FONT_SIZE,
   loadAppSettingsFromStorage as loadAppSettingsFromStoragePure,
@@ -49,13 +52,16 @@ export {
   DEFAULT_APP_SETTINGS,
   DEFAULT_CLIENT_SETTINGS,
   DEFAULT_CODE_FONT_SIZE,
+  DEFAULT_CONTENT_FONT_SIZE,
   DEFAULT_TERMINAL_SCROLLBACK_LINES,
   DEFAULT_THEME_PREFERENCE,
   DEFAULT_UI_BASE_FONT_SIZE,
   MAX_CODE_FONT_SIZE,
+  MAX_CONTENT_FONT_SIZE,
   MAX_TERMINAL_SCROLLBACK_LINES,
   MAX_UI_BASE_FONT_SIZE,
   MIN_CODE_FONT_SIZE,
+  MIN_CONTENT_FONT_SIZE,
   MIN_TERMINAL_SCROLLBACK_LINES,
   MIN_UI_BASE_FONT_SIZE,
   parseClampedFontSize,