Add Promtail service to Docker Compose and update Loki configuration

- Introduced a new Promtail service in `docker-compose.observability.yml` for log collection.
- Configured Promtail with necessary volumes and command for log processing.
- Updated `loki-config.yml` to include `allow_structured_metadata` setting for enhanced metadata handling.

scripts/observability/logs.sh

@@ -0,0 +1,11 @@
+#!/bin/bash
+# EN: View observability stack logs
+# VI: Xem log của observability stack
+
+set -e
+
+# Source OS helper
+source "$(dirname "$0")/../utils/os-helper.sh"
+
+cd infra/observability
+run_compose logs -f

scripts/observability/start.sh

@@ -0,0 +1,30 @@
+#!/bin/bash
+# EN: Start observability stack
+# VI: Khởi động observability stack
+
+set -e
+
+# Source OS helper
+source "$(dirname "$0")/../utils/os-helper.sh"
+
+echo "🚀 Starting Observability Stack..."
+
+# Check if network exists, create if not
+if ! docker network ls | grep -q "microservices-network"; then
+    echo "Creating network 'microservices-network'..."
+    docker network create microservices-network
+fi
+
+# Resolve project root (assuming script is in scripts/observability)
+PROJECT_ROOT="$(cd "$(dirname "$0")/../.." && pwd)"
+cd "$PROJECT_ROOT/infra/observability"
+
+run_compose up -d
+
+echo ""
+echo "✅ Observability stack started!"
+echo "---------------------------------------------------"
+echo "📊 Grafana:    http://localhost:3001 (admin/admin)"
+echo "📈 Prometheus: http://localhost:9090"
+echo "🪵 Loki:       http://localhost:3100"
+echo "---------------------------------------------------"

scripts/observability/stop.sh

@@ -0,0 +1,15 @@
+#!/bin/bash
+# EN: Stop observability stack
+# VI: Dừng observability stack
+
+set -e
+
+# Source OS helper
+source "$(dirname "$0")/../utils/os-helper.sh"
+
+echo "🛑 Stopping Observability Stack..."
+
+cd infra/observability
+run_compose down
+
+echo "✅ Observability stack stopped."