Add freemium variant C: archetype persistence, dashboard banner, lesson gate

- User.archetype/utmSource/utmMedium/utmCampaign fields + migration
- register flow reads ?archetype/?utm_* and saves them on the User row
- dashboard ArchetypeBanner: per-archetype 'твой путь' block
- lesson gate after wow-moment lesson (WOW_MOMENT_LESSON_ID=obs-start-l2-006) → tripwire + full-course offer

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/lib/auth.ts

@@ -71,6 +71,11 @@ export const auth = betterAuth({
         defaultValue: "student",
         input: false,
       },
+      archetype: {
+        type: "string",
+        required: false,
+        input: false,
+      },
     },
   },
 });