- Change LinkedAccount unique constraint to (userId, serviceId, accountId)
- Add linkedAccountId to StreamDestination for per-account targeting
- OAuth callbacks upsert by accountId so different accounts create new rows
- Delete endpoint changed to /providers/accounts/:id
- getDecryptedToken resolves tokens by linkedAccountId instead of serviceId
- /start transition wrapped in try-catch (enableAutoStart compatibility)
- /end always attempts YouTube complete transition regardless of plan status
- autoDetectEndedPlans loads tokens per-destination
