On PostgreSQL the logs table is a RANGE-partitioned table on created_at
owned by pg_partman; GORM AutoMigrate would alter its composite primary
key (id, created_at) and create redundant per-partition indexes,
breaking startup. Extract ensureLogTable() to skip AutoMigrate on
PostgreSQL (existence check only) while keeping the original behavior
on SQLite/MySQL. The dedicated LOG_SQL_DSN PostgreSQL branch follows
the same rule. Ship the matching postgres-partman image (Dockerfile +
01-partition.sql) that creates and maintains the partitioned table via
pg_partman + pg_cron.

Co-Authored-By: ZCode <noreply@anthropic.com>