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/connector.go

@@ -50,7 +50,7 @@ func createConnector(configFile string) CreateConnectorFunc {
 		if err != nil {
 			return nil, err
 		}
-		defer dbFile.Close()
+		defer func() { _ = dbFile.Close() }()
 
 		dec := yaml.NewDecoder(dbFile)
 		cfg := Config{}