Add heartbeat nudge on player join/leave events

Introduces a mechanism to trigger an extra heartbeat shortly after a player connects or disconnects, with a 1s minimum cooldown to prevent spamming. Also makes the serverId field in PendingVotesResponse nullable to tolerate missing values from some backends.

Update release.yml

Update release.yml

Update README.md

Update README.md

Add GitHub Actions workflow for build and release

Introduces a workflow that builds a shaded JAR on pushes to main, computes a version based on the current UTC date and time, and creates a GitHub release with the generated artifact.