v0.2.0

Added

• pg_stat_checkpointer collector (PostgreSQL 17+) - checkpoint operations
• pg_stat_io collector (PostgreSQL 16+) - I/O statistics by backend type
• pg_stat_wal collector (PostgreSQL 14+) - WAL generation statistics
• pg_postmaster_start_time() collector - server startup timestamp
• pg_stat_database per-database collector - conflicts, deadlocks, temp files