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/server/server.go

@@ -0,0 +1,131 @@
+package server
+
+import (
+	"context"
+	"fmt"
+	"net/http"
+	"time"
+
+	"github.com/gin-gonic/gin"
+	"git.dcentral.systems/toolz/goplt/internal/health"
+	"git.dcentral.systems/toolz/goplt/internal/metrics"
+	"git.dcentral.systems/toolz/goplt/pkg/config"
+	"git.dcentral.systems/toolz/goplt/pkg/errorbus"
+	"git.dcentral.systems/toolz/goplt/pkg/logger"
+)
+
+// Server wraps the HTTP server and Gin router.
+type Server struct {
+	httpServer *http.Server
+	router     *gin.Engine
+}
+
+// NewServer creates a new HTTP server with all middleware and routes.
+func NewServer(
+	cfg config.ConfigProvider,
+	log logger.Logger,
+	healthRegistry *health.Registry,
+	metricsRegistry *metrics.Metrics,
+	errorBus errorbus.ErrorPublisher,
+) (*Server, error) {
+	// Set Gin mode
+	env := cfg.GetString("environment")
+	if env == "production" {
+		gin.SetMode(gin.ReleaseMode)
+	}
+
+	router := gin.New()
+
+	// Add middleware (order matters!)
+	router.Use(RequestIDMiddleware())
+	router.Use(LoggingMiddleware(log))
+	router.Use(PanicRecoveryMiddleware(errorBus))
+	router.Use(metricsRegistry.HTTPMiddleware())
+	router.Use(CORSMiddleware())
+
+	// Request timeout middleware (optional, can be configured per route if needed)
+	// router.Use(TimeoutMiddleware(timeout))
+
+	// Register core routes
+	registerRoutes(router, healthRegistry, metricsRegistry)
+
+	// Get server configuration
+	port := cfg.GetInt("server.port")
+	if port == 0 {
+		port = 8080
+	}
+	host := cfg.GetString("server.host")
+	if host == "" {
+		host = "0.0.0.0"
+	}
+
+	readTimeout := cfg.GetDuration("server.read_timeout")
+	if readTimeout == 0 {
+		readTimeout = 30 * time.Second
+	}
+
+	writeTimeout := cfg.GetDuration("server.write_timeout")
+	if writeTimeout == 0 {
+		writeTimeout = 30 * time.Second
+	}
+
+	addr := fmt.Sprintf("%s:%d", host, port)
+
+	httpServer := &http.Server{
+		Addr:         addr,
+		Handler:      router,
+		ReadTimeout:  readTimeout,
+		WriteTimeout: writeTimeout,
+		IdleTimeout:  120 * time.Second,
+	}
+
+	return &Server{
+		httpServer: httpServer,
+		router:     router,
+	}, nil
+}
+
+// registerRoutes registers all core routes.
+func registerRoutes(
+	router *gin.Engine,
+	healthRegistry *health.Registry,
+	metricsRegistry *metrics.Metrics,
+) {
+	// Health endpoints
+	router.GET("/healthz", func(c *gin.Context) {
+		status := healthRegistry.LivenessCheck(c.Request.Context())
+		if status.Status == "healthy" {
+			c.JSON(http.StatusOK, status)
+		} else {
+			c.JSON(http.StatusServiceUnavailable, status)
+		}
+	})
+
+	router.GET("/ready", func(c *gin.Context) {
+		status := healthRegistry.ReadinessCheck(c.Request.Context())
+		if status.Status == "healthy" {
+			c.JSON(http.StatusOK, status)
+		} else {
+			c.JSON(http.StatusServiceUnavailable, status)
+		}
+	})
+
+	// Metrics endpoint
+	router.GET("/metrics", gin.WrapH(metricsRegistry.Handler()))
+}
+
+// Start starts the HTTP server.
+func (s *Server) Start() error {
+	return s.httpServer.ListenAndServe()
+}
+
+// Shutdown gracefully shuts down the HTTP server.
+func (s *Server) Shutdown(ctx context.Context) error {
+	return s.httpServer.Shutdown(ctx)
+}
+
+// Router returns the Gin router (for adding additional routes).
+func (s *Server) Router() *gin.Engine {
+	return s.router
+}
+