refactor: env-var overrides, error handling, and cleanup for testability

[amitb0ra]

Summary

Extracts server-side bug fixes, cleanup, and env-var overrides into a standalone PR

Changes

app.js

• Env-var path overrides — LEADERBOARD_CONFIG_PATH, LEADERBOARD_DATA_PATH, LEADERBOARD_LOG_PATH, LEADERBOARD_ADMINDATA_PATH, LEADERBOARD_CONFIG_BACKUP_PATH, LEADERBOARD_PORT
• LEADERBOARD_SKIP_REFRESH=1 — skip spawning refresh.js child process (useful for testing and dry-run setups)
• Pass res to Util.post() calls — enables proper error responses on malformed JSON (see Util.js below)
• Fix hardcoded ./admindata.json in login handler → use the admindataPath variable (was already defined but not used in one spot)
• Move findContributor from inline function to Util.findContributor (deduplication)
• module.exports = { server } — export the HTTP server for programmatic use

Util.js

• post(req, res, callback) — respond with 400 { message: 'Invalid JSON body' } on malformed POST body instead of silently hanging (same issue identified in fix: add log / output message notifying operator when Github token has expired #126 by @srijnabhargav)
• findContributor() — moved here from app.js

API.js

• Remove process.exit() on bad GitHub credentials — log the error and return instead (prevents the entire server from crashing on a single bad token check)
• Support LEADERBOARD_CONFIG_PATH env var for config resolution

Cleanup

• Remove stale .dockerignore (Docker support was removed in a previous PR)
• Remove dead tests/access.sh and tests/api-call-tests.sh (brute-force stress scripts hitting a defunct external URL)

Merge order

1. This PR first (source changes)
2. PR test: add e2e test suite #127 second (test suite, depends on this)

[Sing-Li]

It is a pity to add ENV var JUST TO SUPPORT TESTING.

Please look into the npm .dotenv library and make this PR a support for .env files during deployment. (in addition to just support testing)

I am totally against combining code generator suggested hallucinations into one PR. For example, the fix in the callback() JSON parse is simply nonsense.

Please remove all other fixes or mods that has nothing to do with supporting dotenv, then test to make sure .env files are actually supported. Thanks.

[Sing-Li]

closing this since you didn't reuse it.