Update Docker images and add healthcheck (#69)

Summary for .devcontainer/docker-compose.yml:
Added startup coordination so the app waits for Postgres to become healthy and Redis to start.
Added a Postgres healthcheck using pg_isready to improve container readiness detection.
Pinned Postgres from latest to postgres:17 for a more stable, reproducible dev environment.
Pinned Redis to redis:7-alpine, which is a smaller, versioned image and can improve image pull time.
Removed the obsolete top-level Compose version field to align with modern Docker Compose conventions.
Kept the original network_mode: service:db behavior, so the app’s networking model is unchanged.

Author: msangapu-msft

.devcontainer/docker-compose.yml

@@ -1,5 +1,3 @@
-version: "3"
-
 services:
   app:
     build:
@@ -9,27 +7,38 @@ services:
     volumes:
       - ..:/workspace:cached
 
-    # Overrides default command so things don't shut down after the process ends.
+    # Keep the development container running.
     command: sleep infinity
 
-    # Runs app on the same network as the database container, allows "forwardPorts" in devcontainer.json function.
+    # Start supporting services before the app container.
+    depends_on:
+      db:
+        condition: service_healthy
+      redis:
+        condition: service_started
+
     network_mode: service:db
 
   db:
-    image: postgres:latest
+    image: postgres:17
     restart: unless-stopped
+
     volumes:
       - postgres-data:/var/lib/postgresql/data
+
     environment:
       POSTGRES_DB: app
       POSTGRES_USER: app_user
       POSTGRES_PASSWORD: app_password
 
-    # Add "forwardPorts": ["5432"] to **devcontainer.json** to forward PostgreSQL locally.
-    # (Adding the "ports" property to this file will not forward from a Codespace.)
+    healthcheck:
+      test: ["CMD-SHELL", "pg_isready -U app_user -d app"]
+      interval: 5s
+      timeout: 5s
+      retries: 10
 
   redis:
-    image: redis
+    image: redis:7-alpine
     restart: unless-stopped
 
 volumes: