Multi-tier streak milestones, success page upgrade & bug fixes

Posting streak now tracks unique days posted instead of total post count — a more meaningful measure of consistency

Posting streak now tracks unique days posted instead of total post count — a more meaningful measure of consistency
New multi-tier milestone system: First 5 posts → 2 weeks → 1 month → 1 quarter → 1 year → 2 years, with completed badges and a progress bar for the current tier
Success page now shows your streak progress with a motivational message, plus a "Create another post" button linking to your next story prompt
Fixed infinite API loop on the Calendar page that was causing excessive rate-limit errors