fix(gamification): use canonical getRank for rank badge criterion

[SoloDrex52]

⚠️ base-red inherited: #15306

Summary

src/lib/gamification/badges.ts carried a private copy of the leaderboard rank query that duplicated getRank() in src/lib/db/gamification.ts, with one behavioral difference: the local copy returned Infinity for a key with no leaderboard entry, while the canonical function returns 0.

This PR drops the local copy and has the rank badge criterion call the canonical getRank(). Because the canonical function reports "unranked" as 0, the criterion now checks rank > 0 && rank <= threshold — a straight swap would have let 0 <= threshold award rank badges (e.g. community-leader) to every key that never scored.

Tests

New: tests/unit/gamification/badge-rank-criteria.test.ts

• unranked key → getRank() === 0 and community-leader is not unlocked
• key at rank 1 → community-leader is unlocked

Validation (Hard Rule #18):

• node --import tsx/esm --test tests/unit/gamification/badge-rank-criteria.test.ts → 2/2 pass
• Mutation check: removing the rank > 0 && guard makes the unranked test fail (1 fail / 1 pass); guard restored
• node --import tsx/esm --test tests/unit/gamification/*.test.ts → 120/120 pass (18 files, incl. leaderboard.test.ts, badges.test.ts)

[SoloDrex52]

Hi @diegosouzapw — this is my first PR from a fork, so the CI, Quality Gates, semgrep and API Route Typecheck workflows are waiting on maintainer approval (action_required). Could you approve the workflow runs when you get a chance? Thanks!