Add email background worker command

Description

This PR introduces background email processing so transactional mail is no longer sent inside the web request.

Emails are written to email_jobs, notified via Redis (cdli:queue:email), and delivered by bin/cake email_worker. When the queue is disabled, mail is still sent inline so environments without a worker keep working.

Technicalities

Queue + worker

• New bin/cake email_worker command (--once for testing)
• Consumes Redis with BRPOP, claims rows with FOR UPDATE
• Falls back to DB polling when Redis is empty or a push was missed
• Handles phpredis BRPOP timeout ([]) correctly
• Shared EmailJobDispatcher for worker and sync fallback
• Supported actions: welcome, resetPassword, adminNewUser, adminCrowdsourcingPrivilege, contributionDeclined
• Transient failures retry with backoff (1 → 2 → 4 min) up to max_attempts, then failed
• Permanent failures (UndeliverableEmailException) are marked cancelled
• Watchdog reclaims stuck processing jobs after 10 minutes; exhausted attempts are failed instead of reclaimed forever
• Fail-fast if email_jobs is missing (config/schema/email_jobs.sql)

Request-path safety

• Gated by CDLI_EMAIL_QUEUE_ENABLED / EmailQueue.enabled (default: false)
• Forgot-password uses soft success copy and revokes the reset token if enqueue fails
• Reset URL is built in the web request and stored in the job payload

Dev infrastructure

• app_email_worker service (dev/gea/mpi)
• Depends on MariaDB, Redis, and Postfix

Tests

• EmailWorkerCommandTest: claim / send / retry / fail / cancel / watchdog / priority / duplicate prevention
• EmailQueueServiceTest: enqueue + sync fallback
• EmailJobsTableTest: payload / allow-list validation

Fakes: FakeRedisForWorker, TimeoutFakeRedisForWorker, TestableEmailWorkerCommand, RecordingEmail