feat: introduces proper job queueing

[gusfcarvalho]

The PR introducing digests neglected the fact a typical CCF setup will run a number of replicas of the API pod

This means notifications, emails, etc will all come up as a multiple of the number of active replicas.

This PR introduces a proper job queueing mechanism centrally defined in Postgres (with the help of river queue).

[Copilot]

Pull request overview

This PR introduces a proper job queueing mechanism using River to prevent duplicate notifications and emails in multi-replica deployments. Previously, each API pod replica would independently send emails and notifications, resulting in duplicates multiplied by the number of replicas.

Changes:

• Adds River-based job queue backed by PostgreSQL for centralized job processing
• Replaces direct email sending with job enqueueing in digest and auth handlers
• Introduces worker service that processes email and digest jobs with configurable concurrency
• Migrates digest scheduling from cron-based to River's periodic jobs

Reviewed changes

Copilot reviewed 15 out of 16 changed files in this pull request and generated 11 comments.

Show a summary per file

File	Description
internal/service/worker/service.go	New worker service that manages River client, workers, and job processing
internal/service/worker/jobs.go	Job definitions and worker functions for email and digest processing
internal/service/worker/service_test.go	Basic tests for worker service initialization
internal/config/worker.go	Configuration for worker service including concurrency and retry settings
internal/config/config.go	Integration of worker configuration into main config
internal/service/digest/service.go	Updated to enqueue digest emails via worker service with fallback
internal/api/handler/auth/auth.go	Updated to enqueue password reset emails via worker service with fallback
internal/api/handler/auth/api.go	Modified to accept and pass worker service to auth handler
internal/service/scheduler/cron.go	Added ParseCronNext utility function for cron parsing
cmd/run.go	Initializes and starts worker service, handles circular dependency with digest service
cmd/digest.go	Updated digest command to pass nil worker service
go.mod, go.sum	Added River queue dependencies and updated pgx to v5.8.0
*_test.go files	Updated test setup to pass nil or properly initialized services

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[Copilot]

Pull request overview

Copilot reviewed 15 out of 16 changed files in this pull request and generated 6 comments.

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[Copilot]

Pull request overview

Copilot reviewed 16 out of 17 changed files in this pull request and generated 10 comments.

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