D3: prune pyth_live 1m bars older than retention window (dry-run by default)

Daily retention prune: removes pyth_live 1m bars older than pyth_live_1m_retention_days (default 30d). Coarser rollups (15m+) are NEVER pruned.

DRY-RUN BY DEFAULT (execute=False) until the founder explicitly enables automated pruning by flipping the lambda to execute=True. Flipping to execute=True is a FOUNDER DECISION — it is irreversible for the deleted rows. Do not change execute=True without explicit founder go-ahead.

pg_cron schedule: daily at 03:00 UTC (0003_d3_live_rollup_jobs.sql). Dead-man 2x = 48h.