feat(app-expo): tiered large-text presets with English-friendly default

Replace the boolean large-text flag with three global typography tiers,
defaulting new installs to the smallest tier when English is in effect
while preserving legacy storage and Chinese defaults. Add a profile
sub-screen to pick the tier and unit tests for storage resolution.

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

app-expo/src/i18n/locales/en/profile.json

@@ -6,8 +6,16 @@
   "appExperience": {
     "language": "Language",
     "languageDesc": "Display language",
-    "largeText": "Large Text",
-    "largeTextDesc": "Make reading easier",
+    "largeText": "Large text",
+    "largeTextDesc": "Standard, large, or extra-large",
+    "largeTextLevel": {
+      "standard": "Standard",
+      "standardDesc": "Comfortable default for most screens",
+      "large": "Large",
+      "largeDesc": "Larger body text and headings app-wide",
+      "extraLarge": "Extra large",
+      "extraLargeDesc": "One more step up from Large"
+    },
     "nightMode": "Night Mode",
     "nightModeDesc": "Use dark theme",
     "theme": "Theme",

app-expo/src/i18n/locales/zh/profile.json

@@ -7,7 +7,15 @@
     "language": "语言",
     "languageDesc": "应用显示语言",
     "largeText": "大字模式",
-    "largeTextDesc": "让阅读更轻松",
+    "largeTextDesc": "标准、大字或更大字号",
+    "largeTextLevel": {
+      "standard": "标准",
+      "standardDesc": "舒适阅读（默认较小）",
+      "large": "大字",
+      "largeDesc": "正文与标题整体放大",
+      "extraLarge": "超大",
+      "extraLargeDesc": "在「大字」基础上再放大一档"
+    },
     "nightMode": "夜间模式",
     "nightModeDesc": "使用深色主题",
     "theme": "主题",