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.

pkg/services/audit.go

@@ -0,0 +1,39 @@
+// Package services provides service client interfaces for inter-service communication.
+package services
+
+import (
+	"context"
+)
+
+// AuditServiceClient is the interface for communicating with the Audit Service.
+type AuditServiceClient interface {
+	// Record records an audit log entry.
+	Record(ctx context.Context, entry *AuditLogEntry) error
+
+	// Query queries audit logs based on filters.
+	Query(ctx context.Context, filters *AuditLogFilters) ([]AuditLogEntry, error)
+}
+
+// AuditLogEntry represents an audit log entry.
+type AuditLogEntry struct {
+	UserID     string            `json:"user_id"`
+	Action     string            `json:"action"`   // e.g., "user.create", "user.update"
+	Resource   string            `json:"resource"` // e.g., "user", "role"
+	ResourceID string            `json:"resource_id"`
+	IPAddress  string            `json:"ip_address"`
+	UserAgent  string            `json:"user_agent"`
+	Metadata   map[string]string `json:"metadata"`
+	Timestamp  int64             `json:"timestamp"`
+}
+
+// AuditLogFilters contains filters for querying audit logs.
+type AuditLogFilters struct {
+	UserID     *string `json:"user_id,omitempty"`
+	Action     *string `json:"action,omitempty"`
+	Resource   *string `json:"resource,omitempty"`
+	ResourceID *string `json:"resource_id,omitempty"`
+	StartTime  *int64  `json:"start_time,omitempty"`
+	EndTime    *int64  `json:"end_time,omitempty"`
+	Limit      int     `json:"limit"`  // Max number of results
+	Offset     int     `json:"offset"` // Pagination offset
+}