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/logger/zap_logger.go

@@ -4,6 +4,7 @@ import (
 	"context"
 
 	"git.dcentral.systems/toolz/goplt/pkg/logger"
+	"go.opentelemetry.io/otel/trace"
 	"go.uber.org/zap"
 	"go.uber.org/zap/zapcore"
 )
@@ -87,6 +88,19 @@ func (zl *zapLogger) WithContext(ctx context.Context) logger.Logger {
 		fields = append(fields, zap.String("user_id", userID))
 	}
 
+	// Extract trace ID from OpenTelemetry context
+	span := trace.SpanFromContext(ctx)
+	if span.SpanContext().IsValid() {
+		traceID := span.SpanContext().TraceID().String()
+		spanID := span.SpanContext().SpanID().String()
+		if traceID != "" {
+			fields = append(fields, zap.String("trace_id", traceID))
+		}
+		if spanID != "" {
+			fields = append(fields, zap.String("span_id", spanID))
+		}
+	}
+
 	if len(fields) == 0 {
 		return zl
 	}