refactor: Align Epic 0 & Epic 1 with true microservices architecture

Refactor core kernel and infrastructure to support true microservices
architecture where services are independently deployable.

Phase 1: Core Kernel Cleanup
- Remove database provider from CoreModule (services create their own)
- Update ProvideHealthRegistry to not depend on database
- Add schema support to database client (NewClientWithSchema)
- Update main entry point to remove database dependency
- Core kernel now provides only: config, logger, error bus, health, metrics, tracer, service registry

Phase 2: Service Registry Implementation
- Create ServiceRegistry interface (pkg/registry/registry.go)
- Implement Consul registry (internal/registry/consul/consul.go)
- Add Consul dependency (github.com/hashicorp/consul/api)
- Add registry configuration to config/default.yaml
- Add ProvideServiceRegistry() to DI container

Phase 3: Service Client Interfaces
- Create service client interfaces:
  - pkg/services/auth.go - AuthServiceClient
  - pkg/services/identity.go - IdentityServiceClient
  - pkg/services/authz.go - AuthzServiceClient
  - pkg/services/audit.go - AuditServiceClient
- Create ServiceClientFactory (internal/client/factory.go)
- Create stub gRPC client implementations (internal/client/grpc/)
- Add ProvideServiceClientFactory() to DI container

Phase 4: gRPC Service Definitions
- Create proto files for all core services:
  - api/proto/auth.proto
  - api/proto/identity.proto
  - api/proto/authz.proto
  - api/proto/audit.proto
- Add generate-proto target to Makefile

Phase 5: API Gateway Implementation
- Create API Gateway service entry point (cmd/api-gateway/main.go)
- Create Gateway implementation (services/gateway/gateway.go)
- Add gateway configuration to config/default.yaml
- Gateway registers with Consul and routes requests to backend services

All code compiles successfully. Core services (Auth, Identity, Authz, Audit)
will be implemented in Epic 2 using these foundations.

internal/client/grpc/audit_client.go

@@ -0,0 +1,33 @@
+// Package grpc provides gRPC client implementations for service clients.
+package grpc
+
+import (
+	"context"
+	"fmt"
+
+	"git.dcentral.systems/toolz/goplt/pkg/registry"
+	"git.dcentral.systems/toolz/goplt/pkg/services"
+)
+
+// AuditClient implements AuditServiceClient using gRPC.
+// This is a stub implementation - will be fully implemented when proto files are generated in Phase 4.
+type AuditClient struct {
+	registry registry.ServiceRegistry
+}
+
+// NewAuditClient creates a new gRPC client for the Audit Service.
+func NewAuditClient(reg registry.ServiceRegistry) (services.AuditServiceClient, error) {
+	return &AuditClient{
+		registry: reg,
+	}, nil
+}
+
+// Record records an audit log entry.
+func (c *AuditClient) Record(ctx context.Context, entry *services.AuditLogEntry) error {
+	return fmt.Errorf("not implemented: proto files not yet generated")
+}
+
+// Query queries audit logs based on filters.
+func (c *AuditClient) Query(ctx context.Context, filters *services.AuditLogFilters) ([]services.AuditLogEntry, error) {
+	return nil, fmt.Errorf("not implemented: proto files not yet generated")
+}