fix(autocert): ensure extra certificate registration and renewal scheduling

Extra providers were not being properly initialized during NewProvider(),
causing certificate registration and renewal scheduling to be skipped.

- Add ConfigExtra type with idx field for provider indexing
- Add MergeExtraConfig() for inheriting main provider settings
- Add setupExtraProviders() for recursive extra provider initialization
- Refactor NewProvider to return error and call setupExtraProviders()
- Add provider-scoped logger with "main" or "extra[N]" name
- Add batch operations: ObtainCertIfNotExistsAll(), ObtainCertAll()
- Add ForceExpiryAll() with completion tracking via WaitRenewalDone()
- Add RenewMode (force/ifNeeded) for controlling renewal behavior
- Add PrintCertExpiriesAll() for logging all provider certificate expiries

Summary of staged changes:
- config.go: Added ConfigExtra type, MergeExtraConfig(), recursive validation with path uniqueness checking
- provider.go: Added provider indexing, scoped logger, batch cert operations, force renewal with completion tracking, RenewMode control
- setup.go: New file with setupExtraProviders() for proper extra provider initialization
- setup_test.go: New tests for extra provider setup
- multi_cert_test.go: New tests for multi-certificate functionality
- renew.go: Updated to use new provider API with error handling
- state.go: Updated to handle NewProvider error return

internal/config/state.go

@@ -272,6 +272,7 @@ func (state *state) initAutoCert() error {
 	autocertCfg := state.AutoCert
 	if autocertCfg == nil {
 		autocertCfg = new(autocert.Config)
+		_ = autocertCfg.Validate()
 	}
 
 	user, legoCfg, err := autocertCfg.GetLegoConfig()
@@ -279,12 +280,19 @@ func (state *state) initAutoCert() error {
 		return err
 	}
 
-	state.autocertProvider = autocert.NewProvider(autocertCfg, user, legoCfg)
-	if err := state.autocertProvider.Setup(); err != nil {
-		return fmt.Errorf("autocert error: %w", err)
-	} else {
-		state.autocertProvider.ScheduleRenewal(state.task)
+	p, err := autocert.NewProvider(autocertCfg, user, legoCfg)
+	if err != nil {
+		return err
 	}
+
+	if err := p.ObtainCertIfNotExistsAll(); err != nil {
+		return err
+	}
+
+	p.ScheduleRenewalAll(state.task)
+	p.PrintCertExpiriesAll()
+
+	state.autocertProvider = p
 	return nil
 }