feat: Add env example drift check for app and service packages

[CollinsKRO]

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[karagozemin]

Thanks for the PR. I rechecked the merge ref from the maintainer account, but the new drift check is currently failing.

Commands run:

git diff --check master...pr-217-merge
node scripts/check-env-docs.mjs

git diff --check is clean, but the new script exits non-zero:

✗ 4 env var(s) missing from env.example
APP_PRIVATE_KEY
SERVICE_BEARER_TOKEN
HTLC_PREIMAGE
VITE_FRONTEND_URL

Please either document those vars in env.example or add narrowly justified allowlist entries if they are test-only/internal. Also please keep the scope focused: this PR is for env example drift, but it currently changes resolver/src/commands/check.ts and overlaps the resolver preflight/check JSON work from #216/#219. If that resolver command change is not required for env drift, please remove it.