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/identity.proto

@@ -0,0 +1,134 @@
+syntax = "proto3";
+
+package identity.v1;
+
+option go_package = "git.dcentral.systems/toolz/goplt/api/proto/generated/identity/v1;identityv1";
+
+// IdentityService provides user management operations.
+service IdentityService {
+  // GetUser retrieves a user by ID.
+  rpc GetUser(GetUserRequest) returns (GetUserResponse);
+  
+  // GetUserByEmail retrieves a user by email address.
+  rpc GetUserByEmail(GetUserByEmailRequest) returns (GetUserByEmailResponse);
+  
+  // CreateUser creates a new user.
+  rpc CreateUser(CreateUserRequest) returns (CreateUserResponse);
+  
+  // UpdateUser updates an existing user.
+  rpc UpdateUser(UpdateUserRequest) returns (UpdateUserResponse);
+  
+  // DeleteUser deletes a user.
+  rpc DeleteUser(DeleteUserRequest) returns (DeleteUserResponse);
+  
+  // VerifyEmail verifies a user's email address using a verification token.
+  rpc VerifyEmail(VerifyEmailRequest) returns (VerifyEmailResponse);
+  
+  // RequestPasswordReset requests a password reset token.
+  rpc RequestPasswordReset(RequestPasswordResetRequest) returns (RequestPasswordResetResponse);
+  
+  // ResetPassword resets a user's password using a reset token.
+  rpc ResetPassword(ResetPasswordRequest) returns (ResetPasswordResponse);
+}
+
+// User represents a user in the system.
+message User {
+  string id = 1;
+  string email = 2;
+  string username = 3;
+  string first_name = 4;
+  string last_name = 5;
+  bool email_verified = 6;
+  int64 created_at = 7;
+  int64 updated_at = 8;
+}
+
+// GetUserRequest contains a user ID.
+message GetUserRequest {
+  string id = 1;
+}
+
+// GetUserResponse contains a user.
+message GetUserResponse {
+  User user = 1;
+}
+
+// GetUserByEmailRequest contains an email address.
+message GetUserByEmailRequest {
+  string email = 1;
+}
+
+// GetUserByEmailResponse contains a user.
+message GetUserByEmailResponse {
+  User user = 1;
+}
+
+// CreateUserRequest contains user data for creation.
+message CreateUserRequest {
+  string email = 1;
+  string username = 2;
+  string password = 3;
+  string first_name = 4;
+  string last_name = 5;
+}
+
+// CreateUserResponse contains the created user.
+message CreateUserResponse {
+  User user = 1;
+}
+
+// UpdateUserRequest contains user data for update.
+message UpdateUserRequest {
+  string id = 1;
+  optional string email = 2;
+  optional string username = 3;
+  optional string first_name = 4;
+  optional string last_name = 5;
+}
+
+// UpdateUserResponse contains the updated user.
+message UpdateUserResponse {
+  User user = 1;
+}
+
+// DeleteUserRequest contains a user ID.
+message DeleteUserRequest {
+  string id = 1;
+}
+
+// DeleteUserResponse indicates success.
+message DeleteUserResponse {
+  bool success = 1;
+}
+
+// VerifyEmailRequest contains a verification token.
+message VerifyEmailRequest {
+  string token = 1;
+}
+
+// VerifyEmailResponse indicates success.
+message VerifyEmailResponse {
+  bool success = 1;
+}
+
+// RequestPasswordResetRequest contains an email address.
+message RequestPasswordResetRequest {
+  string email = 1;
+}
+
+// RequestPasswordResetResponse indicates success.
+message RequestPasswordResetResponse {
+  bool success = 1;
+}
+
+// ResetPasswordRequest contains a reset token and new password.
+message ResetPasswordRequest {
+  string token = 1;
+  string new_password = 2;
+}
+
+// ResetPasswordResponse indicates success.
+message ResetPasswordResponse {
+  bool success = 1;
+}
+