feat: add /api/version endpoint with IMAGE_TAG; validate in ci healthcheck

backend/app/routes/version.py

@@ -0,0 +1,13 @@
+import os
+from flask import Blueprint, jsonify
+
+version_bp = Blueprint("version", __name__)
+
+
+@version_bp.get("/api/version")
+def get_version():
+    """Returns the running image tag — injected at deploy time via IMAGE_TAG env var."""
+    return jsonify({
+        "version": os.environ.get("IMAGE_TAG", "dev"),
+        "env":     os.environ.get("FLASK_ENV", "development"),
+    })