Title: Implement a global leaderboard with local caching

[Mkalbani]

Description

Add an optional leaderboard feature so players can compare scores. Since there's no backend yet, start with a local, file-based leaderboard, structured so a future networked backend can be swapped in without changing the calling API.

Acceptance Criteria

• Leaderboard trait with a LocalFileLeaderboard implementation
• Leaderboard entries store player name, puzzle type, score, and timestamp
• --leaderboard CLI command displays top 10 entries, sortable by score or recency
• Entries persist across sessions in a documented file location
• Trait is designed so a future RemoteLeaderboard (e.g. HTTP-backed) can be added without breaking callers
• Tests cover insertion, sorting, and top-N retrieval

[ebubeb683-ship-it]

Hello boss, Please assign this issue to me. i checked it out and im confident i will solve it
my eta is 4 hours

[Menjay7]

Hi! I came across this issue and would love to work on it. I have experience with similar tasks and I'm confident I can investigate, implement a clean solution, and thoroughly test it before submitting a PR. If the issue is still open, I would appreciate it if you could assign it to me. I’ll prioritize this immediately and ensure a reliable solution is delivered as soon as possible. Thank you!

[VerifiedFlemzy1]

Hello boss, Please assign this issue to me. I checked it out and I am confident I will solve it
my eta is 2 hours

[jaynomyaro]

Hi! I’m a full-stack developer with a strong blockchain background, and I’m confident I can resolve this issue quickly and effectively. I’ll deliver a clean, reliable solution with immediate attention to detail, ensuring it’s completed as soon as possible. Please assign it to me—I’m ready to get started right away.

[grantfox-oss]

🦊 GrantFox — @VerifiedFlemzy1 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 #30)
2. Your PR will be reviewed by the ThinknetCollective maintainers

Good luck! Track your progress on GrantFox.