fix(database): correct metrics and improve error handling

- Fix metrics double-counting: track deltas for WaitCount/WaitDuration
  instead of adding cumulative values each tick
- Replace fmt.Printf with structured logging in pool monitor
- Add PoolOptions validation (MaxConns > 0, MinConns >= 0)
- Warn when DATABASE_URI overrides non-default PoolOptions
- Improve findAndParseConfig to report all tried files and errors
- Remove dead code in pgdb/config.go (unreachable host default)
- Fix errcheck lint issues for file.Close() calls
- Add context parameter to OpenDBMonitor() (breaking change)

database/pool.go

@@ -51,9 +51,9 @@ func OpenDBWithConfigFile(ctx context.Context, configFile string) (*sql.DB, erro
 
 // OpenDBMonitor opens a database connection with monitor-specific defaults
 // This is a convenience function for Monitor package compatibility
-func OpenDBMonitor() (*sql.DB, error) {
+func OpenDBMonitor(ctx context.Context) (*sql.DB, error) {
 	options := MonitorConfigOptions()
-	return OpenDB(context.Background(), options)
+	return OpenDB(ctx, options)
 }
 
 // findConfigFile searches for the first existing config file from the list