test: add unit tests for all badges and CI workflow on badge changes #546

PR #545 introduced the first unit test (tests/badges.test.cjs) covering the SPRINTER badge. We should expand this to cover all 8 badges with positive and negative cases, and gate merges with a CI check.

Badges Needing Tests

• HOT_STREAK — earned when data.streak.current >= 7, locked otherwise
• HARD_CARRY — earned when 5+ Hard and 0 Easy solved in most recent 7-day window
• CENTURION — earned when total solved (easy + medium + hard) ≥ 100
• BALANCED — earned when each ≥ 5 and max-min within 5% of max
• UP_LINK — earned when ranks.overall.change >= 5
• TOP_BRASS — earned when ranks.overall.rank <= 10 (excluding --)
• SPEEDRUN — earned when ranks.weekly.rank <= 3 and positive weighted score

SPRINTER is already covered by #545.

CI Workflow

Add a GitHub Actions workflow (.github/workflows/badge-tests.yml) that:

1. Triggers on PRs to main when frontend/js/user/badges.js or tests/badges.test.cjs are changed
2. Runs node --test tests/badges.test.cjs on ubuntu-latest with Node 20
3. Also add a "test" script to package.json: "test": "node --test tests/"

Proposed workflow

name: Badge Tests

on:
  pull_request:
    branches: [main]
    paths:
      - "frontend/js/user/badges.js"
      - "tests/badges.test.cjs"

jobs:
  test:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4

      - uses: actions/setup-node@v4
        with:
          node-version: "20"

      - run: node --test tests/badges.test.cjs

Linked PRs

Follows up on #545