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.

api/proto/authz.proto

@@ -0,0 +1,80 @@
+syntax = "proto3";
+
+package authz.v1;
+
+option go_package = "git.dcentral.systems/toolz/goplt/api/proto/generated/authz/v1;authzv1";
+
+// AuthzService provides authorization operations.
+service AuthzService {
+  // Authorize checks if a user has a specific permission and returns an error if not.
+  rpc Authorize(AuthorizeRequest) returns (AuthorizeResponse);
+  
+  // HasPermission checks if a user has a specific permission.
+  rpc HasPermission(HasPermissionRequest) returns (HasPermissionResponse);
+  
+  // GetUserPermissions returns all permissions for a user.
+  rpc GetUserPermissions(GetUserPermissionsRequest) returns (GetUserPermissionsResponse);
+  
+  // GetUserRoles returns all roles for a user.
+  rpc GetUserRoles(GetUserRolesRequest) returns (GetUserRolesResponse);
+}
+
+// Permission represents a permission in the system.
+message Permission {
+  string id = 1;
+  string code = 2;
+  string name = 3;
+  string description = 4;
+}
+
+// Role represents a role in the system.
+message Role {
+  string id = 1;
+  string name = 2;
+  string description = 3;
+  repeated string permissions = 4; // Permission codes
+}
+
+// AuthorizeRequest contains user ID and permission to check.
+message AuthorizeRequest {
+  string user_id = 1;
+  string permission = 2;
+}
+
+// AuthorizeResponse indicates authorization result.
+message AuthorizeResponse {
+  bool authorized = 1;
+  string message = 2;
+}
+
+// HasPermissionRequest contains user ID and permission to check.
+message HasPermissionRequest {
+  string user_id = 1;
+  string permission = 2;
+}
+
+// HasPermissionResponse indicates if the user has the permission.
+message HasPermissionResponse {
+  bool has_permission = 1;
+}
+
+// GetUserPermissionsRequest contains a user ID.
+message GetUserPermissionsRequest {
+  string user_id = 1;
+}
+
+// GetUserPermissionsResponse contains all permissions for the user.
+message GetUserPermissionsResponse {
+  repeated Permission permissions = 1;
+}
+
+// GetUserRolesRequest contains a user ID.
+message GetUserRolesRequest {
+  string user_id = 1;
+}
+
+// GetUserRolesResponse contains all roles for the user.
+message GetUserRolesResponse {
+  repeated Role roles = 1;
+}
+