Public profile visibility at 100 questions + subscription

[SanAlexis]

Context

At 100 questions + active subscription, the user's profile becomes publicly visible to other Active members in the Lookup Layer:

• Heatmap data
• Accuracy trends
• Exam track
• Session frequency
• Confidence calibration

Acceptance criteria

• Profile visibility toggled by lookup_unlocked flag on User
• lookup_unlocked set to true when questions_answered >= 100 AND subscription_status = 'active'
• Public profile view shows meaningful data (not just a shell)
• Profile hidden again if subscription lapses (Dormant state)