feat(shutdown): drain WebSocket clients on SIGTERM

[Ferryx349]

Description

• On SIGTERM, /readyz returns 503 so load balancers stop routing new traffic
• Rejects new WebSocket connections and drains existing clients with Nostr CLOSED and graceful WS close
• Bounded by WS_DRAIN_TIMEOUT_MS (default 30s); primary forwards SIGTERM to cluster workers and waits for exit

Related Issue

Fixes :- #772

Motivation and Context

How Has This Been Tested?

Screenshots (if appropriate):

Types of changes

• Non-functional change (docs, style, minor refactor)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my code changes.
• I added a changeset, or this is docs-only and I added an empty changeset.
• All new and existing tests passed.

[changeset-bot]

🦋 Changeset detected

Latest commit: d1ea235

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
nostream	Minor

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[coveralls]

coverage: 72.207% (-0.08%) from 72.283% — feat/ws-drain into main