Two tokio tasks spawned at startup that sweep their respective
tables on a weekly cadence (design notes §3 #9 + §4 retention).
Both use `FOR UPDATE SKIP LOCKED` on the claim query so concurrent
sweepers in cluster mode (v1.3+) don't fight each other.
Defaults: 30 days for dead_letters, 7 days for abandoned_executions.
Both env-overridable via `PICLOUD_DEAD_LETTER_RETENTION_DAYS` and
`PICLOUD_ABANDONED_EXECUTIONS_RETENTION_DAYS` (loaded into
`TriggerConfig::from_env` from commit 5).
Per-tick batch cap (5_000 rows) so a sweep can't lock up the table
in a single transaction; the inner loop continues until 0 rows
affected, after which the outer tick waits for the next week.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
