[Feature Request] Add Duolingo-style "Streak Freeze" support (`&freeze=true`)

Feature Proposal

Add an optional Streak Freeze parameter (similar to Duolingo's streak freeze mechanism) to prevent users from losing their current streak due to 1-2 missed days (e.g., during weekends, holidays, or short personal breaks).

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How It Works

1. New Query Parameter: Users can pass &freeze=true in their card URL.
2. Fairness Limit: To keep streaks authentic and prevent abuse, the maximum allowable freeze days would be hardcoded (e.g., maximum 2 or 3 days).
3. Behavior: If a user misses a day with 0 contributions, the calculation logic consumes 1 freeze token instead of immediately resetting currentStreak to 0.