feat(epic1): implement core infrastructure (stories 1.1-1.5)

Implemented Epic 1 core kernel and infrastructure stories:

Story 1.1: Enhanced DI Container
- Added providers for database, health, metrics, and error bus
- Extended CoreModule to include all core services

Story 1.2: Database Layer with Ent ORM
- Created Ent schema for User, Role, Permission, AuditLog entities
- Implemented many-to-many relationships (User-Role, Role-Permission)
- Created database client wrapper with connection pooling
- Added database provider to DI container with migration support

Story 1.3: Health Monitoring and Metrics System
- Implemented health check registry and interface
- Added database health checker
- Created Prometheus metrics system with HTTP instrumentation
- Added health and metrics providers to DI container

Story 1.4: Error Handling and Error Bus
- Implemented channel-based error bus
- Created ErrorPublisher interface
- Added error bus provider with lifecycle management

Story 1.5: HTTP Server Foundation
- Created HTTP server with Gin framework
- Implemented comprehensive middleware stack:
  - Request ID generation
  - Structured logging
  - Panic recovery with error bus integration
  - Prometheus metrics collection
  - CORS support
- Registered core routes: /healthz, /ready, /metrics
- Integrated with FX lifecycle for graceful shutdown

All components are integrated via DI container and ready for use.

internal/health/database.go

@@ -0,0 +1,26 @@
+package health
+
+import (
+	"context"
+
+	"git.dcentral.systems/toolz/goplt/internal/infra/database"
+	"git.dcentral.systems/toolz/goplt/pkg/health"
+)
+
+// DatabaseChecker implements health checks for the database.
+type DatabaseChecker struct {
+	client *database.Client
+}
+
+// NewDatabaseChecker creates a new database health checker.
+func NewDatabaseChecker(client *database.Client) health.HealthChecker {
+	return &DatabaseChecker{
+		client: client,
+	}
+}
+
+// Check performs a database health check.
+func (d *DatabaseChecker) Check(ctx context.Context) error {
+	return d.client.Ping(ctx)
+}
+

internal/health/registry.go

@@ -0,0 +1,74 @@
+package health
+
+import (
+	"context"
+	"sync"
+
+	"git.dcentral.systems/toolz/goplt/pkg/health"
+)
+
+// Registry manages health checkers.
+type Registry struct {
+	checkers map[string]health.HealthChecker
+	mu       sync.RWMutex
+}
+
+// NewRegistry creates a new health check registry.
+func NewRegistry() *Registry {
+	return &Registry{
+		checkers: make(map[string]health.HealthChecker),
+	}
+}
+
+// Register registers a health checker with the given name.
+func (r *Registry) Register(name string, checker health.HealthChecker) {
+	r.mu.Lock()
+	defer r.mu.Unlock()
+	r.checkers[name] = checker
+}
+
+// Check performs health checks for all registered checkers.
+func (r *Registry) Check(ctx context.Context) health.HealthStatus {
+	r.mu.RLock()
+	defer r.mu.RUnlock()
+
+	components := make([]health.ComponentStatus, 0, len(r.checkers))
+	overallStatus := health.StatusHealthy
+
+	for name, checker := range r.checkers {
+		err := checker.Check(ctx)
+		status := health.StatusHealthy
+		errorMsg := ""
+
+		if err != nil {
+			status = health.StatusUnhealthy
+			errorMsg = err.Error()
+			overallStatus = health.StatusUnhealthy
+		}
+
+		components = append(components, health.ComponentStatus{
+			Name:   name,
+			Status: status,
+			Error:  errorMsg,
+		})
+	}
+
+	return health.HealthStatus{
+		Status:     overallStatus,
+		Components: components,
+	}
+}
+
+// LivenessCheck performs a basic liveness check (no dependencies).
+func (r *Registry) LivenessCheck(ctx context.Context) health.HealthStatus {
+	// Liveness is always healthy if the service is running
+	return health.HealthStatus{
+		Status: health.StatusHealthy,
+	}
+}
+
+// ReadinessCheck performs a readiness check (includes dependency checks).
+func (r *Registry) ReadinessCheck(ctx context.Context) health.HealthStatus {
+	return r.Check(ctx)
+}
+