feat(functions): implement cron scheduling with BullMQ

[kkopanidis]

Problem

functionType: 'cron' was accepted by the admin API and UI but never ran on a schedule. The runtime fell through to the event-bus path and subscribed to a channel named after the cron expression, so scheduled functions silently never executed.

Summary

• Add BullMQ functions-cron-queue with idempotent syncCronJobs() on every refreshRoutes()
• Stable repeatable job IDs (cron-{functionId}); orphan cleanup on delete/type change
• Canonical inputs.cronPattern with legacy inputs.event alias; admin validation on upload/patch
• Cron invocations reuse the VM sandbox, FunctionExecutions, and existing metrics
• Migration copies legacy inputs.event → inputs.cronPattern for existing cron docs

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update
• Refactor
• Build-related changes
• Other (please describe)

Does this PR introduce a breaking change?

• Yes
• No

The PR fulfills these requirements:

• It's submitted to the main branch

If adding a new feature, the PR's description includes:

• A convincing reason for adding this feature

Test plan

• Create a cron function via Admin API (*/5 * * * *); confirm FunctionExecutions records appear within ~5 minutes
• Update the cron pattern; confirm cadence changes without duplicate Redis repeatable keys
• Delete the function; confirm executions stop after refresh
• Verify functionType: 'event' still subscribes to the bus (no regression)
• Set functions module active: false; confirm queue drains and ticks stop
• Rolling deploy with two replicas: single execution per tick