Complete Paperboy Stripe and cadence attribution

[cgallic]

Closes the production QA gap where verified attribution reached KaiBuilds but omitted cadence and Stripe trial/paid/cancel/failure lifecycle events never entered the durable outbox.

• Adds cadence and weekly day to every durable lifecycle payload
• Queues trial start and cancellation from processed subscription webhooks
• Queues payment failure and only positive paid invoices as purchase
• Carries the real server-confirmed amount, currency, and invoice identity
• Keeps trial starts distinct from purchases

Verification: 96 tests, Ruff, and full-package mypy pass.