fix: add pyproject.toml for multi-mode deployment compliance

pyproject.toml

@@ -0,0 +1,22 @@
+[build-system]
+requires = ["setuptools>=61.0"]
+build-backend = "setuptools.build_meta"
+
+[project]
+name = "lifeline-ai"
+version = "1.0.0"
+description = "LifeLine AI OpenEnv healthcare triage environment"
+readme = "README.md"
+requires-python = ">=3.11"
+authors = [
+    { name = "Mallikarjun" }
+]
+
+dependencies = [
+    "fastapi",
+    "uvicorn",
+    "pydantic"
+]
+
+[tool.setuptools]
+packages = ["backend"]