Consolidate streaks.js and streaks-advanced.js

[vayungodara]

Problem

streaks.js and streaks-advanced.js contain duplicated streak calculation logic. This makes maintenance harder and increases risk of the two diverging.

What to change

• Audit both files and identify shared logic
• Extract common streak utilities into a single module (e.g. lib/streaks.ts)
• Have both current consumers import from the shared module
• Remove duplicated code

Acceptance criteria

• Single source of truth for streak logic
• No duplicated calculation functions
• Existing functionality unchanged (verify with manual testing)

Label: tech-debt | Priority: low

[vayungodara]

After auditing both files: streaks.js handles core calculations + visualization, streaks-advanced.js handles user features (freezes, risk detection, milestones). No duplication — they have clear separation of concerns with a clean import relationship. Closing as not needed.