feat: Add OpenTelemetry OTLP HTTP receiver

- Add POST /v1/traces endpoint for OTLP JSON trace ingestion
- Convert OTLP spans to internal format and save to PostgreSQL
- Manual JSON parsing (no Go 1.24 dependencies)
- Add Node.js instrumentation example with Express
- Add Python instrumentation example with Flask
- Auto-instrumentation support for both languages

examples/otel-python/app.py

@@ -0,0 +1,168 @@
+"""
+═══════════════════════════════════════════════════════════
+📱 Example Flask App with OpenTelemetry
+═══════════════════════════════════════════════════════════
+
+Run with:
+    python app.py
+
+Or with auto-instrumentation:
+    opentelemetry-instrument python app.py
+"""
+
+import os
+import time
+import random
+import atexit
+from flask import Flask, jsonify, request
+from opentelemetry import trace
+from opentelemetry.trace import Status, StatusCode
+from opentelemetry.instrumentation.flask import FlaskInstrumentor
+
+# Initialize tracing BEFORE creating Flask app
+from tracing import init_tracing, get_tracer, shutdown
+
+init_tracing()
+tracer = get_tracer()
+
+app = Flask(__name__)
+
+# Auto-instrument Flask
+FlaskInstrumentor().instrument_app(app)
+
+# Register shutdown handler
+atexit.register(shutdown)
+
+# Simulated database
+users = [
+    {"id": 1, "name": "Alice", "email": "alice@example.com"},
+    {"id": 2, "name": "Bob", "email": "bob@example.com"},
+    {"id": 3, "name": "Charlie", "email": "charlie@example.com"},
+]
+
+
+@app.route('/health')
+def health():
+    """Health check endpoint."""
+    return jsonify({"status": "healthy", "service": "python-example"})
+
+
+@app.route('/users')
+def get_users():
+    """Get all users with custom span."""
+    with tracer.start_as_current_span("db.query.users") as span:
+        span.set_attribute("db.system", "memory")
+        span.set_attribute("db.operation", "SELECT")
+        
+        # Simulate database latency
+        time.sleep(random.uniform(0.01, 0.1))
+        
+        span.set_attribute("db.row_count", len(users))
+        span.set_status(Status(StatusCode.OK))
+        
+        return jsonify({"users": users})
+
+
+@app.route('/users/<int:user_id>')
+def get_user(user_id: int):
+    """Get user by ID."""
+    with tracer.start_as_current_span("db.query.user_by_id") as span:
+        span.set_attribute("db.system", "memory")
+        span.set_attribute("db.operation", "SELECT")
+        span.set_attribute("user.id", user_id)
+        
+        # Simulate database latency
+        time.sleep(random.uniform(0.01, 0.05))
+        
+        user = next((u for u in users if u["id"] == user_id), None)
+        
+        if not user:
+            span.set_status(Status(StatusCode.ERROR, "User not found"))
+            return jsonify({"error": "User not found"}), 404
+        
+        span.set_status(Status(StatusCode.OK))
+        return jsonify({"user": user})
+
+
+@app.route('/orders', methods=['POST'])
+def create_order():
+    """Create order with nested spans."""
+    with tracer.start_as_current_span("order.create") as parent_span:
+        try:
+            data = request.get_json() or {}
+            items = data.get("items", [])
+            
+            # Step 1: Validate inventory
+            with tracer.start_as_current_span("inventory.check") as span:
+                span.set_attribute("order.items", len(items))
+                time.sleep(random.uniform(0.05, 0.1))
+                span.set_status(Status(StatusCode.OK))
+            
+            # Step 2: Process payment
+            with tracer.start_as_current_span("payment.process") as span:
+                span.set_attribute("payment.method", "credit_card")
+                time.sleep(random.uniform(0.1, 0.2))
+                span.set_status(Status(StatusCode.OK))
+            
+            # Step 3: Create order record
+            with tracer.start_as_current_span("db.insert.order") as span:
+                time.sleep(random.uniform(0.02, 0.05))
+                order_id = hex(int(time.time() * 1000))[2:]
+                span.set_attribute("order.id", order_id)
+                span.set_status(Status(StatusCode.OK))
+            
+            parent_span.set_status(Status(StatusCode.OK))
+            return jsonify({"orderId": order_id, "status": "created"})
+            
+        except Exception as e:
+            parent_span.set_status(Status(StatusCode.ERROR, str(e)))
+            parent_span.record_exception(e)
+            return jsonify({"error": str(e)}), 500
+
+
+@app.route('/error')
+def trigger_error():
+    """Trigger error for testing."""
+    span = trace.get_current_span()
+    error = Exception("Simulated error for testing")
+    
+    span.record_exception(error)
+    span.set_status(Status(StatusCode.ERROR, str(error)))
+    
+    return jsonify({"error": str(error)}), 500
+
+
+@app.route('/external-call')
+def external_call():
+    """Make external HTTP call (demonstrates distributed tracing)."""
+    import requests
+    
+    with tracer.start_as_current_span("external.http.call") as span:
+        span.set_attribute("http.url", "https://httpbin.org/get")
+        
+        try:
+            # Note: requests auto-instrumentation propagates trace context
+            response = requests.get("https://httpbin.org/get", timeout=5)
+            span.set_attribute("http.status_code", response.status_code)
+            span.set_status(Status(StatusCode.OK))
+            return jsonify({"status": "ok", "external_status": response.status_code})
+        except Exception as e:
+            span.record_exception(e)
+            span.set_status(Status(StatusCode.ERROR, str(e)))
+            return jsonify({"error": str(e)}), 500
+
+
+if __name__ == '__main__':
+    port = int(os.getenv('PORT', 5000))
+    print(f"""
+🚀 Example app listening on http://localhost:{port}
+
+Try these endpoints:
+  GET  http://localhost:{port}/health
+  GET  http://localhost:{port}/users
+  GET  http://localhost:{port}/users/1
+  POST http://localhost:{port}/orders
+  GET  http://localhost:{port}/error
+  GET  http://localhost:{port}/external-call
+""")
+    app.run(host='0.0.0.0', port=port, debug=False)