feat(epic1): complete OpenTelemetry integration and add verification documentation

Story 1.6: OpenTelemetry Distributed Tracing
- Implemented tracer initialization with stdout (dev) and OTLP (prod) exporters
- Added HTTP request instrumentation via Gin middleware
- Integrated trace ID correlation in structured logs
- Added tracing configuration to config files
- Registered tracer provider in DI container

Documentation and Setup:
- Created Docker Compose setup for PostgreSQL database
- Added comprehensive Epic 1 summary with verification instructions
- Added Epic 0 summary with verification instructions
- Linked summaries in documentation index and epic READMEs
- Included detailed database testing instructions
- Added Docker Compose commands and troubleshooting guide

All Epic 1 stories (1.1-1.6) are now complete. Story 1.7 depends on Epic 2.

internal/di/providers.go

@@ -13,10 +13,12 @@ import (
 	"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/observability"
 	"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.opentelemetry.io/otel/trace"
 	"go.uber.org/fx"
 )
 
@@ -156,6 +158,54 @@ func ProvideMetrics() fx.Option {
 	})
 }
 
+// ProvideTracer creates an FX option that provides the OpenTelemetry tracer.
+func ProvideTracer() fx.Option {
+	return fx.Provide(func(cfg config.ConfigProvider, lc fx.Lifecycle) (trace.TracerProvider, error) {
+		enabled := cfg.GetBool("tracing.enabled")
+		if !enabled {
+			// Return no-op tracer
+			return trace.NewNoopTracerProvider(), nil
+		}
+
+		serviceName := cfg.GetString("tracing.service_name")
+		if serviceName == "" {
+			serviceName = "platform"
+		}
+
+		serviceVersion := cfg.GetString("tracing.service_version")
+		if serviceVersion == "" {
+			serviceVersion = "1.0.0"
+		}
+
+		env := cfg.GetString("environment")
+		if env == "" {
+			env = "development"
+		}
+
+		otlpEndpoint := cfg.GetString("tracing.otlp_endpoint")
+
+		tp, err := observability.InitTracer(context.Background(), observability.Config{
+			Enabled:        enabled,
+			ServiceName:    serviceName,
+			ServiceVersion: serviceVersion,
+			Environment:    env,
+			OTLPEndpoint:   otlpEndpoint,
+		})
+		if err != nil {
+			return nil, fmt.Errorf("failed to initialize tracer: %w", err)
+		}
+
+		// Register lifecycle hook to shutdown tracer
+		lc.Append(fx.Hook{
+			OnStop: func(ctx context.Context) error {
+				return observability.ShutdownTracer(ctx, tp)
+			},
+		})
+
+		return tp, nil
+	})
+}
+
 // ProvideHTTPServer creates an FX option that provides the HTTP server.
 func ProvideHTTPServer() fx.Option {
 	return fx.Provide(func(
@@ -164,9 +214,10 @@ func ProvideHTTPServer() fx.Option {
 		healthRegistry *health.Registry,
 		metricsRegistry *metrics.Metrics,
 		errorBus errorbus.ErrorPublisher,
+		tracer trace.TracerProvider,
 		lc fx.Lifecycle,
 	) (*server.Server, error) {
-		srv, err := server.NewServer(cfg, log, healthRegistry, metricsRegistry, errorBus)
+		srv, err := server.NewServer(cfg, log, healthRegistry, metricsRegistry, errorBus, tracer)
 		if err != nil {
 			return nil, fmt.Errorf("failed to create HTTP server: %w", err)
 		}
@@ -194,7 +245,7 @@ func ProvideHTTPServer() fx.Option {
 }
 
 // CoreModule returns an FX option that provides all core services.
-// This includes configuration, logging, database, error bus, health checks, metrics, and HTTP server.
+// This includes configuration, logging, database, error bus, health checks, metrics, tracing, and HTTP server.
 func CoreModule() fx.Option {
 	return fx.Options(
 		ProvideConfig(),
@@ -203,6 +254,7 @@ func CoreModule() fx.Option {
 		ProvideErrorBus(),
 		ProvideHealthRegistry(),
 		ProvideMetrics(),
+		ProvideTracer(),
 		ProvideHTTPServer(),
 	)
 }