Two related fixes that must land together:
1. config.Load() now starts from DefaultConfig() before unmarshaling
YAML. This ensures missing top-level fields (Performance,
Monitoring, Resolver) use their documented defaults instead of
zero values. Most importantly, file_cache is no longer silently
disabled when users omit the performance: section.
2. startSingleMode() now checks Monitoring.Status.Enabled instead of
Path/Allow to decide whether to register the status endpoint.
Without this change, fix#1 would have caused a regression where
the status handler is registered even when monitoring is disabled,
because DefaultConfig() sets Path and Allow defaults.
Also replace remaining log.Printf in status.go and lua/api_timer.go
with zerolog to follow project logging conventions.
Added tests:
- config/load_test.go: verifies defaults are applied, explicit values
override defaults, and monitoring stays disabled by default.
- server/monitoring_registration_test.go: verifies /_status is only
registered when enabled and remains reachable with static handler
on path: /.
