feat(scoring): add Evergreen playstyle & fix active_years calculation bug

[KrishnaX12]

Description

This PR introduces the new Evergreen playstyle to reward developers for long-term consistency, and also patches a critical bug in the engine's active_years scoring logic.

Changes Made

1. Evergreen Playstyle (lib/scoring/playstyles.ts):
   • Added the Evergreen playstyle using the leaf (🍃) icon.
   • Rewards developers for consistent yearly activity (Base tier: 5 active years, Elite tier: 10 active years).
2. Fixed active_years Logic (lib/github/signals.ts):
   • The Bug: active_years was previously being estimated by looking at the creation and push timestamps of the user's top 100 repositories. This severely undercounted developers (like Linus Torvalds) who commit heavily over many years but only to a small handful of repositories.
   • The Fix: Completely rewrote the active_years logic to calculate directly from the contributionYears payload, ensuring every single calendar year with at least 1 contribution is perfectly counted.
3. Cache Invalidation (lib/scout.ts):
   • Bumped CACHE_VERSION to v3 to globally bust the Redis cache and force all profiles to recalculate their true active_years when this deploys to production.

[KrishnaX12]

@Younesfdj Hey! I updated this PR with the new Evergreen playstyle to reward long-term consistency. I also patched a major bug in the active_years scoring logic that was severely undercounting veteran developers (like Linus).

Tested locally and bumped the cache. Screenshot attached of it working perfectly on Torvalds's profile! Let me know what you think!