Seasonal leaderboard & gamification epochs (`seasons.rs`)

[DevMuhdishaq]

Description
get_top_traders returns an all-time leaderboard. Add time-boxed "seasons" so gamification can reset and reward periodically.

Direction

• Create counter/src/seasons.rs tracking per-season volume/score per user, keyed by season id.
• start_season/end_season (admin), get_season_leaderboard(season_id), get_current_season.
• On season end, snapshot top-N and optionally award badges via rewards.

Acceptance criteria

• Trades accrue to the current season's score.
• Ending a season freezes its leaderboard; a new season starts scores at zero.
• get_season_leaderboard returns correct ranking for a past season.
• Top-N snapshot triggers badge award (asserted via has_badge).
• Tests cover multi-season transitions.

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[GBOYEE]

Hi maintainers, I'd like to take this on (Seasonal leaderboard & gamification epochs (seasons.rs)). I'll implement it to spec and add tests. Will send a PR for this after assignment.

[sadeeq6400]

Good day

I have read the requirements of this issue and i am confident that i can solve this

[grantfox-oss]

🦊 GrantFox — @sadeeq6400 has been assigned to this issue as part of the Official Campaign | FWC26 campaign!

Next steps:

1. Open a Pull Request referencing this issue (e.g., Closes #217)
2. Your PR will be reviewed by the StelTade maintainers

Good luck! Track your progress on GrantFox.

[grantfox-oss]

🎉 This issue has been marked as completed on GrantFox as part of the Official Campaign | FWC26 campaign!

@sadeeq6400's PR #241 was approved and merged by @DevMuhdishaq.

🏆 @sadeeq6400: You earned 35 FoxPoints for this contribution! Your current tier: Explorer (732 total points). Track your full progress on GrantFox.

👏 Great work, @sadeeq6400! Keep contributing to StelTade.