fix(relay): add package-lock.json and improve Dockerfile fallback

[d0zingcat]

Summary

Fixes docker build failure in the relay component caused by missing package-lock.json when npm ci is executed.

Root Cause

• .gitignore was ignoring package-lock.json globally, preventing relay/package-lock.json from being committed.
• relay/Dockerfile invoked npm ci --omit=dev, which strictly requires a package-lock.json file.

Changes

1. Added relay/package-lock.json: Generated lockfile for relay dependencies (ws).
2. Updated .gitignore: Whitelisted !relay/package-lock.json so lockfile is tracked in git.
3. Improved relay/Dockerfile: Added safe fallback (if [ -f package-lock.json ]; then npm ci ...; else npm install ...; fi).

Verification

• Successfully built image via docker build -t synctabs-relay . without error.
• Verified /health endpoint responds with { status: "ok" }.