Streak was incremented on every individual log entry regardless of targetGoal, and had no consecutive-day validation — logging on day 1 and day 3 would produce a streak of 2.

Changes

• calculateHabitStreak() (new) — derives streak by grouping logs by date, filtering to days where count >= targetGoal, then walking backward through sorted dates counting consecutive days from the most recent fully-completed day
• logHabitCompletion() — replaces streak + 1 with a call to calculateHabitStreak() on the current log state, so retroactive completions (filling a gap in past days) are correctly reflected

// targetGoal: 3 — partial completion no longer advances streak
logHabitCompletion(habit.id, today); // count=1, streak=0
logHabitCompletion(habit.id, today); // count=2, streak=0
logHabitCompletion(habit.id, today); // count=3, streak=1 ✓

// Retroactive gap-fill
logHabitCompletion(habit.id, day1); // streak=1
logHabitCompletion(habit.id, day3); // streak=1 (gap at day2)
logHabitCompletion(habit.id, day2); // streak=3 ✓

• Fixes Streak counter incorrect #24

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