[DEPLOY-04] Configure Cloudflare Workers — `joinId` Rotation Cron

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Description

Deploy apps/cron to Cloudflare Workers as a scheduled task for periodic joinId rotation.

Subtasks

• DEPLOY-04-ST-01 Configure wrangler.toml for apps/cron
• DEPLOY-04-ST-02 Deploy Cloudflare Workers scheduled task
• DEPLOY-04-ST-03 Verify cron schedule and rotation logic in production
• DEPLOY-04-ST-04 Set DB connection env vars for Cloudflare Workers

Acceptance Criteria

• DEPLOY-04-AC-01 Cron job runs on schedule
• DEPLOY-04-AC-02 All non-null joinId values rotated simultaneously
• DEPLOY-04-AC-03 Old links invalidated after rotation

Technical Notes

• Docs: TDD#32-appscron-structure
• Relevant files: apps/cron/src/