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/infra/database/client.go

@@ -0,0 +1,87 @@
+package database
+
+import (
+	"context"
+	"database/sql"
+	"fmt"
+	"time"
+
+	"entgo.io/ent/dialect"
+	entsql "entgo.io/ent/dialect/sql"
+	"git.dcentral.systems/toolz/goplt/internal/ent"
+	_ "github.com/lib/pq" // PostgreSQL driver
+)
+
+// Client wraps the Ent client with additional functionality.
+type Client struct {
+	*ent.Client
+	db *sql.DB
+}
+
+// Config holds database configuration.
+type Config struct {
+	DSN              string
+	MaxConnections   int
+	MaxIdleConns     int
+	ConnMaxLifetime  time.Duration
+	ConnMaxIdleTime  time.Duration
+}
+
+// NewClient creates a new Ent client with connection pooling.
+func NewClient(cfg Config) (*Client, error) {
+	// Open database connection
+	db, err := sql.Open("postgres", cfg.DSN)
+	if err != nil {
+		return nil, fmt.Errorf("failed to open database connection: %w", err)
+	}
+
+	// Configure connection pool
+	db.SetMaxOpenConns(cfg.MaxConnections)
+	db.SetMaxIdleConns(cfg.MaxIdleConns)
+	db.SetConnMaxLifetime(cfg.ConnMaxLifetime)
+	db.SetConnMaxIdleTime(cfg.ConnMaxIdleTime)
+
+	// Test connection
+	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+	defer cancel()
+
+	if err := db.PingContext(ctx); err != nil {
+		db.Close()
+		return nil, fmt.Errorf("failed to ping database: %w", err)
+	}
+
+	// Create Ent driver
+	drv := entsql.OpenDB(dialect.Postgres, db)
+
+	// Create Ent client
+	entClient := ent.NewClient(ent.Driver(drv))
+
+	return &Client{
+		Client: entClient,
+		db:     db,
+	}, nil
+}
+
+// Close closes the database connection.
+func (c *Client) Close() error {
+	if err := c.Client.Close(); err != nil {
+		return err
+	}
+	return c.db.Close()
+}
+
+// Migrate runs database migrations.
+func (c *Client) Migrate(ctx context.Context) error {
+	return c.Client.Schema.Create(ctx)
+}
+
+// Ping checks database connectivity.
+func (c *Client) Ping(ctx context.Context) error {
+	return c.db.PingContext(ctx)
+}
+
+// DB returns the underlying *sql.DB for advanced operations.
+func (c *Client) DB() *sql.DB {
+	return c.db
+}
+