Tutor/answers: bare subscripts (S_n, a_1) become Unicode; migration 0022 re-cleans DB text

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

content/seed/curriculum.json

@@ -158704,7 +158704,7 @@
        "lessons": [
         {
          "title": "مقدارِ لگاریتم",
-         "introText": "logb(bᵏ) = k.",
+         "introText": "log پایه‌ی b(bᵏ) = k.",
          "example": "",
          "steps": []
         },
@@ -158716,7 +158716,7 @@
         },
         {
          "title": "معادله‌ی لگاریتمی",
-         "introText": "logb x = k ⇔ x = bᵏ.",
+         "introText": "log پایه‌ی b x = k ⇔ x = bᵏ.",
          "example": "",
          "steps": []
         },