feat: support for watt process runner

[fenos]

What kind of change does this PR introduce?

Feature

What is the new behavior?

• Add Watt support for starting the server in a monitored and multi-CPU system
• Corrected shutdown order and prevented error messages on shutdown

Additional context

Add any other context or screenshots.

[Copilot]

Pull request overview

Adds support for running the service under the Watt/Platformatic process runner (multi-worker), while refining shutdown sequencing to reduce noisy errors and improve cleanup behavior.

Changes:

• Added watt.json runtime configuration and Platformatic/Watt dependencies.
• Updated shutdown handling (SIGTERM/SIGINT) and improved cleanup ordering across queue/pubsub/TUS close paths.
• Adjusted cluster rebalance logic to account for multi-worker setups via a new numWorkers config.

Reviewed changes

Copilot reviewed 8 out of 9 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
watt.json	Adds Watt/Platformatic runtime configuration for multi-worker process management.
src/start/shutdown.ts	Introduces shared graceful shutdown handler and forces exit after shutdown completes.
src/start/server.ts	Uses numWorkers to adjust cluster sizing passed to pool rebalancing.
src/internal/queue/queue.ts	Simplifies queue shutdown by removing reliance on stopped event sequencing.
src/internal/pubsub/postgres.ts	Prevents unlisten calls after pubsub is closed to avoid shutdown errors.
src/http/routes/tus/index.ts	Awaits lock notifier shutdown during Fastify onClose.
src/config.ts	Adds numWorkers parsed from WORKERS_NUM.
package.json	Adds Platformatic/Watt deps and updates Node engine constraint.

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[ferhatelmas]

instead of divide, shouldn't we increase (multiply)? tasks vs tasks * workers

[ferhatelmas]

and related, what happens if there is no change event is triggered?