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/design-tokens.json

@@ -220,6 +220,26 @@
       "lineHeightTight": 28,
       "lineHeightLoose": 34,
       "lineHeightXLoose": 40
+    },
+    "xxlarge": {
+      "headingLarge": 50,
+      "headingMedium": 37,
+      "headingSmall": 32,
+      "titleLarge": 32,
+      "titleMedium": 28,
+      "titleSmall": 24,
+      "bodyLarge": 32,
+      "bodyMedium": 30,
+      "bodySmall": 20,
+      "captionLarge": 20,
+      "captionMedium": 18,
+      "captionSmall": 17,
+      "sectionTitle": 18,
+      "badge": 14,
+      "lineHeightNormal": 34,
+      "lineHeightTight": 32,
+      "lineHeightLoose": 39,
+      "lineHeightXLoose": 46
     }
   }
 }