feat(api): add unified response format utilities (Section 1, Step 1.1-1.3)

- Create response.py with success_response(), error_response(), paginated_response()
- Add unit tests for all response utility functions
- Create /api/ping/ health check endpoint using new format
- Update __init__.py to export response functions
- All changes are non-breaking - existing code unaffected

This implements Section 1 Task 1 from API-IMPLEMENTATION-PLAN-SECTION1.md
Ready for testing before applying to existing endpoints.

Ref: unified-api/API-IMPLEMENTATION-PLAN-SECTION1.md

backend/igny8_core/api/views.py

@@ -0,0 +1,33 @@
+"""
+API Views for IGNY8 Core
+
+Health check and utility endpoints.
+"""
+
+from rest_framework.views import APIView
+from django.utils import timezone
+from igny8_core.api.response import success_response
+
+
+class PingView(APIView):
+    """
+    Health check endpoint for API availability.
+    
+    Returns simple pong response to verify API is live.
+    This endpoint uses the new unified response format.
+    """
+    permission_classes = []  # Public endpoint - no authentication required
+    
+    def get(self, request):
+        """
+        Return health check response in unified format.
+        """
+        return success_response(
+            data={
+                "pong": True,
+                "time": timezone.now().isoformat(),
+                "version": "1.0.0"
+            },
+            message="API is live"
+        )
+