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/di/providers.go

@@ -3,11 +3,19 @@ package di
 import (
 	"context"
 	"fmt"
+	"net/http"
 	"os"
+	"time"
 
 	configimpl "git.dcentral.systems/toolz/goplt/internal/config"
+	errorbusimpl "git.dcentral.systems/toolz/goplt/internal/errorbus"
+	"git.dcentral.systems/toolz/goplt/internal/health"
+	"git.dcentral.systems/toolz/goplt/internal/infra/database"
 	loggerimpl "git.dcentral.systems/toolz/goplt/internal/logger"
+	"git.dcentral.systems/toolz/goplt/internal/metrics"
+	"git.dcentral.systems/toolz/goplt/internal/server"
 	"git.dcentral.systems/toolz/goplt/pkg/config"
+	"git.dcentral.systems/toolz/goplt/pkg/errorbus"
 	"git.dcentral.systems/toolz/goplt/pkg/logger"
 	"go.uber.org/fx"
 )
@@ -55,12 +63,147 @@ func ProvideLogger() fx.Option {
 	})
 }
 
+// ProvideDatabase creates an FX option that provides the database client.
+func ProvideDatabase() fx.Option {
+	return fx.Provide(func(cfg config.ConfigProvider, lc fx.Lifecycle) (*database.Client, error) {
+		dsn := cfg.GetString("database.dsn")
+		if dsn == "" {
+			return nil, fmt.Errorf("database DSN is not configured")
+		}
+
+		maxConns := cfg.GetInt("database.max_connections")
+		if maxConns == 0 {
+			maxConns = 25
+		}
+
+		maxIdleConns := cfg.GetInt("database.max_idle_connections")
+		if maxIdleConns == 0 {
+			maxIdleConns = 5
+		}
+
+		connMaxLifetime := cfg.GetDuration("database.conn_max_lifetime")
+		if connMaxLifetime == 0 {
+			connMaxLifetime = 5 * time.Minute
+		}
+
+		connMaxIdleTime := cfg.GetDuration("database.conn_max_idle_time")
+		if connMaxIdleTime == 0 {
+			connMaxIdleTime = 10 * time.Minute
+		}
+
+		dbClient, err := database.NewClient(database.Config{
+			DSN:             dsn,
+			MaxConnections:  maxConns,
+			MaxIdleConns:    maxIdleConns,
+			ConnMaxLifetime: connMaxLifetime,
+			ConnMaxIdleTime: connMaxIdleTime,
+		})
+		if err != nil {
+			return nil, fmt.Errorf("failed to create database client: %w", err)
+		}
+
+		// Register lifecycle hooks
+		lc.Append(fx.Hook{
+			OnStart: func(ctx context.Context) error {
+				// Run migrations on startup
+				if err := dbClient.Migrate(ctx); err != nil {
+					return fmt.Errorf("failed to run database migrations: %w", err)
+				}
+				return nil
+			},
+			OnStop: func(ctx context.Context) error {
+				return dbClient.Close()
+			},
+		})
+
+		return dbClient, nil
+	})
+}
+
+// ProvideErrorBus creates an FX option that provides the error bus.
+func ProvideErrorBus() fx.Option {
+	return fx.Provide(func(log logger.Logger, lc fx.Lifecycle) (errorbus.ErrorPublisher, error) {
+		bufferSize := 100 // Can be made configurable
+		bus := errorbusimpl.NewChannelBus(log, bufferSize)
+
+		// Register lifecycle hook to close the bus on shutdown
+		lc.Append(fx.Hook{
+			OnStop: func(ctx context.Context) error {
+				return bus.Close()
+			},
+		})
+
+		return bus, nil
+	})
+}
+
+// ProvideHealthRegistry creates an FX option that provides the health check registry.
+func ProvideHealthRegistry() fx.Option {
+	return fx.Provide(func(dbClient *database.Client) (*health.Registry, error) {
+		registry := health.NewRegistry()
+		
+		// Register database health checker
+		registry.Register("database", health.NewDatabaseChecker(dbClient))
+
+		return registry, nil
+	})
+}
+
+// ProvideMetrics creates an FX option that provides the Prometheus metrics registry.
+func ProvideMetrics() fx.Option {
+	return fx.Provide(func() *metrics.Metrics {
+		return metrics.NewMetrics()
+	})
+}
+
+// ProvideHTTPServer creates an FX option that provides the HTTP server.
+func ProvideHTTPServer() fx.Option {
+	return fx.Provide(func(
+		cfg config.ConfigProvider,
+		log logger.Logger,
+		healthRegistry *health.Registry,
+		metricsRegistry *metrics.Metrics,
+		errorBus errorbus.ErrorPublisher,
+		lc fx.Lifecycle,
+	) (*server.Server, error) {
+		srv, err := server.NewServer(cfg, log, healthRegistry, metricsRegistry, errorBus)
+		if err != nil {
+			return nil, fmt.Errorf("failed to create HTTP server: %w", err)
+		}
+
+		// Register lifecycle hooks
+		lc.Append(fx.Hook{
+			OnStart: func(ctx context.Context) error {
+				// Start server in a goroutine
+				go func() {
+					if err := srv.Start(); err != nil && err != http.ErrServerClosed {
+						log.Error("HTTP server error",
+							logger.String("error", err.Error()),
+						)
+					}
+				}()
+				return nil
+			},
+			OnStop: func(ctx context.Context) error {
+				return srv.Shutdown(ctx)
+			},
+		})
+
+		return srv, nil
+	})
+}
+
 // CoreModule returns an FX option that provides all core services.
-// This includes configuration and logging.
+// This includes configuration, logging, database, error bus, health checks, metrics, and HTTP server.
 func CoreModule() fx.Option {
 	return fx.Options(
 		ProvideConfig(),
 		ProvideLogger(),
+		ProvideDatabase(),
+		ProvideErrorBus(),
+		ProvideHealthRegistry(),
+		ProvideMetrics(),
+		ProvideHTTPServer(),
 	)
 }